Super Glue or cyanoacrylate glue or CA glue (whatever you choose to call it) is some amazing stuff. I have been using it more and more in the shop and seem to find new uses for it every day. When combined with an activator to make this already super glue that much more super, its crazy how fun and helpful it can be. Lately it seems like if something is broken or just not quite right, I’m reaching for the super glue. And, in an age of immediate gratification, it seems to fit right in.
CA glue, which most everyone knows as super glue, has recently developed quite the following, leading to a wide variety of choices in makers and products. The biggest expansion in product lines has come in the form of different viscosities, from thin to thick, which allow for greater control and the ability to be used in more situations. The thin derivation is great for making repairs where something is cracked but not really in two separate pieces and the thicker varieties are great for gap filling, while the medium is a good, all around, gluing choice.
The other advancement, the one which makes super glue super fun, is the addition of spray activators. An activator will make CA glue set up almost immediately, changing the clear, easily flowing liquid into a hard crystalline structure with great adhesive quality. The activator makes CA glue work the way you have always dreamed for glue to work – you have time to get the loose pieces into position and when they are, just shoot them with activator and there they stay. And, the repairs are incredibly strong.
My first introduction to CA glue in woodworking came in the form of a presentation at the St. Louis Woodworkers Guild. The speaker was discussing building intricate handrails, which were made of many small pieces of wood, connected end grain to end grain, to form the curvy bits at the top and bottom of the stairs. He showed how he was able to use nothing but CA glue in the tightest of spots to produce quick, strong and lasting bonds.
End grain joints are notoriously horrible glue joints in any other world, but in the super glue world the joints held up great. He brought in some samples and glued them right in front of our eyes and in just seconds formed a new piece of wood which no one could break. All he did was put the CA glue on one part and sprayed the other with activator. As soon as the two pieces touched, the bond was complete. On joints which required some open time for alignment, he also had the option to use only the CA glue and not shoot the activator until everything was lined up. The glue closest to the surface would dry immediately to hold everything in place and in a short amount of time the glue on the inside of the joint would harden for a complete bond. It is a real game changer in spots which are traditionally very difficult to connect.
Besides simply holding two things together, CA glue also has many other uses. I commonly use it when I am in the final stages of finishing and find voids which need to be filled. If the voids are big, epoxy is usually the choice, but CA glue works great as a type of clear filler between the epoxy and the final finish stages. I typically use the medium or thick variety and hit it with the activator for a speedy surface fill and repair. Once the CA glue sets up it can be sanded and worked like any other plastic finish and then topcoated without issue.
CA glue is also great as a wood hardener. It isn’t uncommon for me to run into wood that is decayed or starting to decay somewhere (especially in spalted or “character” wood) and needs a little support structurally. By soaking the questionable wood with the thin version of CA glue, I can quickly turn a delicate spot into a spot which is as hard as rock and will stay bonded with the surrounding wood. And, again, it happens almost immediately, even without an activator.
Lastly, CA glue can be a finish all by itself. I don’t personally use it as a finish, since I am not a wood turner (you can find out why by clicking here), but I know plenty of people who do. Usually, it is used for smaller projects like pens and bowls, where less-than-perfect wood is a common choice. I suspect it was first used to simply hold burled wood together and then people started to realize that it filled voids and finished nicely. After that, it was a logical step to start using it as the finish and take advantage of its strength and immediacy.
The big negative for me, when I started using super glue on a regular basis, was the possibility of accidentally glueing myself or getting glued to something else. I think everyone knows that super glue bonds immediately to skin and it seems like everyone is always warning everyone else to not get it on their skin, so I used it with trepidation. However, since using CA glue now, almost every day, I can tell you that it is much less scary.
I have no problem or concerns with using my raw, ungloved finger to wipe up a drip of super glue like I would any other errant liquid. If you do the same, you just need to be smart about it. If you get it on your hand, don’t immediately grab something – it will stick. Just let it dry and you will have no problem. And, if you do stick your fingers together, don’t freak out. Enjoy the moment and look at your fingers in awe and appreciate how good the glue works on your skin. Then, simply wipe the glue with acetone and you will be unstuck. And, even if you get CA glue on your skin and do nothing about it, the glue will start to peel off after a couple of days without causing any pain or damage. It really isn’t as life changing as others might make it out to be. As a matter of fact, I even know a guy (not named here for professional courtesy) who shot CA glue directly in his eye, and though a bit uncomfortable, had no real issues arise from it.
I recommend having three viscosities (thin, medium and thick) of CA glue and a spray activator in your shop at all times, ready to go. Purchase it before you need it, then you will have it on hand when the need arises and you can take advantage of the speed it offers. I guarantee that once you start using CA glue in your shop, you will find a million uses for it too.
Whenever I put a new blade on my sawmill, I fold up the old one to send it out for sharpening. I don’t find the process as awesome as I used to, but it still seems to intrigue others that haven’t seen me do it before. And, I must admit, when I know someone is watching that hasn’t seen me fold up a bandsaw blade before, I do it extra fast and super snappy to make it seem even more dazzling. With a quick flick of my wrists, the 50″ diameter loop of bandsaw blade is reduced to three loops at just 17″, making it easier to handle and ship out.
I learned how to coil a bandsaw blade like this pre-YouTube and over the phone from the kids at Wood-Mizer, who supply and sharpen my blades. It took a few tries to do it the first time and many more to get good at it, but I figured if I could learn it over the phone then I could certainly show others how to do it with visuals. The good news is that like learning to ride a bike, once you get it, you’ve got it.
To prepare, put on some gloves (without holes). Start by holding the blade with each of your hands on the outside of the blade, away from your body and parallel to the ground with the teeth facing up. Imagine that you are holding out a large basketball hoop in front of you waiting for someone else to take a shot. From there, whip the portion of the blade furthest from you towards the ground and just as the blade nears the ground give it a quick jerk up, with a snap. This motion will make the blade start to fold in half, with the teeth going away from you. At the same time that the blade starts to fold in half, simply twist both of your wrists towards the inside of the loop. If your timing is right, you will get to a certain point where the blade no longer wants to fight you and then it will just spring into three loops.
When you are first learning this technique you may find it helpful to get a feel for it by cheating a bit. Start just as described above while standing on carpeting or grass or some other surface that is soft and will grab the teeth of the saw blade (I show it in the photos using a piece of lumber). Now, instead of whipping the blade towards the ground, just drop the end furthest away from you to the ground, so that the blade is now perpendicular to the ground. Use the soft and grabby surface to snag the teeth as you start to lift and push the blade up an away from you. Instead of getting the blade to fold in half with a whip motion, you are now going to get it to fold by pushing against the soft floor. As the blade starts to fold in half, with the teeth away from you, roll your wrists to the inside of the loop, just like described above. Using this method, you will be able to feel the exact point where the blade stops fighting you and happily coils into three loops. You should be able to get a feel for it after just a few times with this “cheating” method and then move on to the fancy, snappy method.
Recently, I got a question from a customer regarding a crack forming in his solid wood countertop. He built the top out of flat sawn white oak lumber and he wanted to figure out what caused the crack and hopefully, how he could repair it. Luckily, the repair is simple (just some glue and clamps), but he really needed to address the cause of the problem or the countertop would most likely crack again.
When he sent me photos of the crack, he also sent me photos of the how he attached it to the cabinets, which was very helpful. The vintage metal cabinets have a bracket in each corner with a hole just large enough for a screw, but not large enough to allow for any movement in the top. In this case, the wood was stuck in place and had no choice but to split when it shrunk in width.
I recommended to simply make the holes in the metal bracket bigger and to add a washer or use a large-headed screw to allow the top to move side to side while still being held down. The secret is to tighten the screws just enough to hold the top in place, but loose enough to allow it to move if the wood starts to pull.
This particular solution was pretty simple, but only because I have seen it many times before, and I knew what caused it. Without understanding how wood moves, the diagnosis wouldn’t be so apparent. Even though most people don’t worry about wood movement as much as I do, I always try to get them to understand the most basic premise, which is that wood moves more in width than it does in length, and you need to allow for that movement.
In woodworking in general, this disparity in movement is referred to as a “cross-grain situation”, when two pieces of wood come together with grain perpendicular to each other, then they want to pull in opposite directions. It happens all of the time in furniture construction, and it must be addressed to avoid catastrophic failures. In the example above, the setup was the same as a cross grain situation because the metal cabinet will not change in any dimension, while the wood moves in width.
When attaching wood tops of any kind, whether it be a wood countertop to a cabinet or a table top to a table base, you need to allow the top to move or it can split. The good news is that there is more than one way to attach a top and still make allowances for this movement.
The first and most common way, as mentioned earlier, is to make an oversized or elongated hole and to make up any differences with a washer or large-headed screw. Assume that any problems will be caused by excessive shrinkage and make sure that your holes are big enough and that your screws are placed in the holes so that the top has room to shrink.
Another method, which I like to use on tables, is to make blocks to fit into dados on the insides of the aprons. They don’t take too long to make and can easily be added wherever necessary. The blocks should be made so that tightening up the screws will just pull the top snug, like a perfect fitting tongue and groove joint and placed with a little separation to make sure nothing binds. They work great, and I think they look great too.
When attaching a top with a propensity to move, understand that all of your attachment points don’t have to have play in them. For example, you can firmly attach a countertop to the front of a cabinet as long as you allow the top to move in the back. Or, on table tops, you might choose to firmly attached the top in the middle of the width and allow the outside edges to move. This is perfectly acceptable and keeps the top centered on the base.
The main point to remember through all of this is to allow the wood to move. You can only really cause a problem if you don’t allow it to move. And remember , if you find that it is moving too much for your liking you can always go back and firm things up once you understand the potential problems.
For a more thorough description of wood movement click on these two earlier posts Have Your Heard About Shrinkage? or Why Quartersawn Lumber is so Stable: The 0-1-2 Rule In Action, to read a link on the subject. I think it is probably the most important subject for any woodworker to fully understand.
I am a woodworker, and as a woodworker I live by a certain set of norms which dictate that I be accurate, but not ridiculously accurate. After all, wood changes size all of the time, so there is a limit to how accurate we can be and how much we should really worry about it. For most of us, a few measurements in a job are critical and the rest of the pieces are fit to look good. We may use measurements as a jumping off point, but it isn’t uncommon to trim a bit here and plane a bit there.
When I am in the shop, I always have a tape measure hanging off of my pocket for anything that needs to be measured. I use it a lot, but mostly for rough measurements, like making sure a piece of wood will be big enough for what I have in mind. I also use it for more critical measurements, but I try my best to find ways to not use measurements when things start to get critical. For example, instead of measuring, I will use a scrap piece of wood as a spacer. That way I don’t need to worry every time about reading the tape measure wrong, and I know that all of my spacing will be very consistent.
As much as I try to avoid being fussy about my measurements, sometimes they need to be a little more accurate. One of the tools where accuracy is important is the planer. If I want 1″ thick wood, I want to know that it is 1″. Now, more engineery people might reach for their calipers, but for those of you like me, with only a tape measures on your belt, I have a very accurate way to make perfectly sized parts – just stack them up.
Here’s the logic. If your measurements are just slightly off, you may not notice it in just one piece, but as you add up the pieces you also add up the differences and they become much more obvious. Just run a scrap piece of wood through the planer, chop it into 3, 4 or 5 pieces, stack them up and measure them. 5 pieces of wood that are 1″ thick should measure 5″ – simple de dimple. If your 1″ thick board isn’t exactly 1″ thick, you will see it, even without calipers, and then you can adjust the thickness.
The beauty of this system is two-fold. First off, you don’t need to worry about having calipers (after all, those are for kids that work at Boeing and have really clean floors). Second, it gives you a more accurate real-world reading of what is coming out of your machine. We all know that a board coming out of the planer has dips and doodles in the wood and can range in thickness depending on the spot that you measure. Adding up several pieces of wood gives you not only a measurement that is accurate, but it is also closer to the average. We are only talking small amounts here, but if you are setting up to plane a bunch of lumber, it is great to know what the bulk of it is going to measure.
I use this system to double-check measurements on other tools as well. It works great on the table saw to make sure that your 3″ wide board is really 3″. Instead of cutting just one sample board 3″ wide and determining that it looks really close, cut 3 or more and add them up. Assuming that you can do a little simple math, you will be able to tell if the 3″ mark is consistently spitting out 3″ boards and not 2-63/64″ boards.
When using my fancy measuring shortcut, there is one important rule to follow. Make sure the tongue on your tape measure is accurate or don’t use the tongue at all. If you don’t trust the tongue on your tape measure then take a reading starting at the 1″ mark to check the distance and then just subtract 1″ from your reading (and then hope that a holiday is quickly approaching that might lend itself to the arrival of a new tape measure).
When customers visit my shop we usually start by talking about their wood needs. If it is someone’s first time to visit I also try to get to know them, what they are looking for and what they are expecting from me. Half of them are just looking for rough cut wood, while the others are looking for wood that is processed a little bit more, perhaps jointed or planed, or even sanded. During our time together I get to understand their needs and abilities, and our discussion usually turns to the tools they have in their shop.
I am often surprised at what tools woodworkers don’t use or own, especially when they are some of the few that I find essential. Sometimes it’s just the difference between hand tool and power tool guys, but sometimes it’s just from lack of experience or the fact that they haven’t given it too much thought. Most likely they just buy tools as they need them and never really considered what tools would give them the most bang for the buck.
Since this is a common conversation, I decided to compile the following list of what I think are the most useful power tools and should be the building blocks of any woodworking shop:
Table saw. Of all of the tools in the shop, the table saw is the most useful and versatile. It excels at making straight cuts, and with the addition of any of a million jigs, can be made to perform an amazing number of tasks with repeatability and precision. I use the table saw for roughing out smaller parts from larger pieces, all the way through trimming parts to final size. The only limit to the table saw is that the piece needs to be small enough to be pushed through it. Above a certain size, the table saw becomes less useful and even impossible to use as the saw needs to be brought to the piece, instead of the piece being brought to the saw.
The table saw is best suited for making rip cuts, which are cuts along the length of the board, but with a crosscutting jig, the table saw can do just as well on crosscuts, which are cuts across the board. I even use the table saw for resawing thick lumber into thinner boards. The bandsaw is usually the tool for resawing, but any lumber under 6″ wide can be resawn on a 10″ table saw by cutting from both sides of the board.
Besides just making through cuts, the table saw can also cut dados, rabbets and other grooves with just a few adjustments. And, with the addition of profiled cutters and a creative mind, the table saw can be used to make all kinds of mouldings, including large crown mouldings.
The table saw also works amazingly well as a table. Mine is big enough to not only hold stuff, but serve as an assembly table when necessary. The table of the table saw is set apart from other tables because it is commonly the only one open and available in the shop. I try to keep it clear enough to actually use, which means that at least part of the top is usually available and ready to be used as a table or maybe even a saw.
Thickness Planer. Running a rough board through the planer is always fun. Even after sending billions of board feet through a planer, it never gets old. The amazing thing is that beyond making the wood look good, the planer can size lumber in ways other tools can’t.
I have met a lot of customers that don’t have a planer. And, while it is possible to operate without one, I believe that once you own one, you will find it hard to believe that you ever ran a shop without it. For me, it is along the same line of thinking for spray guns, where I say, “Stop thinking about buying a spray gun.”
Even if you buy your lumber already planed, you will still encounter many circumstances that require the use of a planer. For example, you might want to build a simple and delicate jewelry box out of small scrap pieces lying around the shop, and you will end up making a small and clunky jewelry box because all of your lumber is 3/4″ thick, and that’s how it is going to stay. That is just the first example. Think about all of the other times that you will pick up a piece of lumber in the shop and it will be the wrong thickness, either just slightly wrong or in an entirely different size category. A planer is a real problem solver and can fix all of that.
If you work with rough lumber, a planer will be absolutely necessary, except for the most rustic of projects. Every piece of rough cut lumber ends up somewhat not straight, not flat and not consistent in thickness, either from variations during the sawing or from stresses which occur while the wood dries. The planer, combined with the jointer, is a one-two punch to remove these variations and produce straight, flat and consistently thick lumber. The reason the planer is ahead of the jointer on this list is that some lumber is straight enough and flat enough to plane without jointing if the job is a little less finicky, thereby skipping the jointer.
Jointer. I use my jointer a lot. When preparing rough lumber it sees as much action as the planer. As a matter of fact, almost every piece of lumber in my shop gets surfaced on the wide face to straighten things out before it even heads to the planer. Without the jointer, my life would just be a crooked, twisty mess of painful attempts to make things seem straight.
One of the misconceptions about planers is that they make lumber straight. They do some straightening, but they don’t make lumber straight. That is what jointers do. Many lumber mills just send rough lumber through the planer allowing the board to exit the machine with the same ups and downs and whoops that is entered with, only now to a consistent thickness. This is especially apparent when gluing up a couple of these roller coaster type of boards and trying to get them to line up. After a couple of those glue-ups, you will swear by lumber that has seen the jointer before the planer, and never skip the jointer.
Besides flattening lumber, the jointer also puts a straight edge on lumber for joining two boards together and for running through other machines. I also use the jointer for making small adjustments during the final fitting of parts like drawer fronts, where small changes can make a big difference.
With these three power tools (and a few hand tools), I feel like I could make about 80% of the jobs that come through my shop on a daily basis. Obviously, some jobs will require more specialized power tools to complete, but these three probably find their way into almost all of my work. With that said, there are a few other tools that I couldn’t imagine being without and I feel need to be added to the list.
Spray gun. Not every woodworking job gets a film finish, but most of mine do. And of those, every one will meet a spray gun. For a million reasons, including making finishing fast and fun, I recommend using a spray gun whenever possible. It will raise your game and make you n0t hate finishing. (Click here to read my thoughts on purchasing a spray gun).
Chop saw (compound miter saw). I do a mix of woodworking from furniture to built-ins and even finish carpentry, and I find myself regularly using the chop saw. Even if used for nothing more than roughly cutting a long board into two shorter ones to fit in a car, this tool earns its keep. It is especially useful (with the help of an outfeed table) on long pieces that are precarious to push through a table saw. But, since a table saw with a jig can perform many of the same functions, this tool doesn’t make it to the essential list. With that said, I expect to have a chop saw wherever I am working, whether it be in the shop or at an install. If this was a post about on-site woodworking and trim carpentry, the chop saw might be the #1 tool.
Impact driver. I am a giant fan of impact drivers. I have been using them for a while now and can’t really remember my life before them (Click here to read more about my introduction to impact drivers). This is the one tool that I always have with me, and I expect to be within easy reach. So much so, that I own three of them and could imagine myself with a couple more. Like the chop saw, if this was a list of on-site or installation tools, the impact driver would be near the top.
Tape measure. I know this isn’t a power tool, but it is the one tool that you should always have with you. It is a pet peeve of mine – if you are planning on building something, or you are actually building it, have a tape measure with you. If you are in the shop, on the job site, or even at Home Depot make sure you have a tape measure with you or at least one very handy (Home Depot probably isn’t the best example, since they have them widely available, but you get the point). Without a tape measure, not much beyond rough work can get done. (Click here to read about my favorite tape measure).
For all of you out there that hate sanding, there is a new fun-to-use tool that takes almost all the work out of it, and may even make it fun. The new “Whirl-Whizz” sander combines the sanding power of four orbital sanders with the joy of playing with your favorite christmas present to make short work of even the most difficult sanding.
“We always had trouble finding anyone that wanted to sand the bottom of our slab tables and other hard to reach surfaces, like wood beams and ceilings,” says Scott Wunder from WunderWoods Custom Hardwoods. “That was until we started using the “Whirl-Whizz.” Now everyone in the shop wants to sand. Our only problem now is making sure that we have enough sandpaper on hand”.
The “Whirl-Whizz” sander looks like a standard hobby drone with just a few modifications, but don’t be fooled, this thing is a real workhorse. The four thin plastic spinning rotors provide the perfect balance between power and finesse by pulling the sander strongly to the surface, but deflecting and riding any slight contour changes throughout the process. The end result is a super smooth, consistently sanded surface that requires no hand sanding – that’s right, no more hand sanding.
“This thing works so good that the guys started using it in places that it was never meant to go,” Wunder continued. “After they figured out how to get it to spots other than the underside of horizontal surfaces, they found it worked better than any sander they had ever used. Before long they were sanding every surface with it, top, bottom, vertical, horizontal – it didn’t matter. If they could get the “Whirl-Whizz” to run into it, then they would sand it.”
As a busy business owner with lots of sanding to get done, Wunder has ordered ten more units to make sure that he always has a sander at the ready. The current average life span of the “Whirl-Whizz” sander, including rotor wear and incidental contact with unintended targets is about 15 minutes, but Wunder expects those numbers to go up as everyone at WunderWoods gets better at operating this new generation of sander. “Every new tool takes a while to master, and this is no different,” Wunder said defending his team. “A new battery will sand for approximately six minutes. As those batteries get older and have to spend more time on the charger, the life-span of each of our units will increase as it is used less. It really is just a matter of time.”
Another benefit to shop owners besides the flawless results is that every “Whirl-Whizz” sander features an on board camera, which can be used for up-close inspection of a surface. By simply pushing a button for a still picture or holding the button for a video, it is now ultra easy to see what is really going on close-up. Many shop managers use the camera system remotely on their phone to make sure that their employees are performing as expected, even when they are away. At WunderWoods however, Scott points out, “We are having so much fun with the “Whirl-Whizz” that I didn’t even know it had a camera.”
Today, I was having a conversation with one of my customers about spraying a conversion varnish (Krystal, from M.L. Campbell) and the problems he was having with getting it to lay down nicely after it was sprayed. He said that he applied is wet enough to blend together and not be rough, but that he had a lot of orange peel in the finish. After discussing the possible causes of the orange peel it became obvious that he needed to add lacquer thinner to the mix, which he did not do.
This customer is new to spraying conversion varnish, which is a two-part mix that sets up and hardens chemically like epoxy, forming a super durable finish. The information on the can talked about the 10:1 ratio of finish to catalyst, but apparently didn’t mention a thing about thinning with lacquer thinner, so he used none. Even if it was mentioned, I assume that he was worried enough about getting the ratio correct (click here to learn how to easily get the proper mixing ratios) and not messing up the mix that he never imagined he could, or even that he should add lacquer thinner.
In this case, my customer was getting orange peel because the finish was too thick for his two-stage turbine. The kids at the finish distributor led him to believe that he shouldn’t need to add thinner, but they did not ask about the power of his spray equipment, assuming that he probably had a turbine strong enough to finely atomize the finish without thinning.
I continued to discuss the need to add thinner with my customer, and pointed out that a non-thinned finish requires more turbine power than he currently has. If he owned a 4-stage or 5-stage turbine, he could probably use the finish without thinner, but not with just a 2-stage. I speak from experience on this one, because my everyday gun is an older 2-stage model, and it requires at least a bit of thinning on almost everything I spray. I am okay with this apparent shortcoming because I am a proponent of applying multiple thin coats, as compared to fewer thick coats, which I believe are just inviting trouble.
As our conversation continued, he asked the million dollar question, “How much lacquer thinner do you add?” For me, the simple answer is, “Until it sprays good,” which is very ambiguous I know, but true. I have an advantage because I have sprayed more than him and I have an idea where I am headed, but I don’t truly know until I shoot a sample board with it and see how things are flowing (which I do every time before I spray the real thing). I spray a sample piece of wood standing up vertically to make sure that I can get a fully wet and flat surface with no runs or sags and to get a feel for how fast I need to move the gun to make all of that happen. If the sample surface looks good, I move on and spray the real thing. If I have issues, it is usually because the finish is a bit thick, so I add lacquer thinner until the finish sprays smoothly without orange peel and without runs.
Another, more technical way to determine the correct amount of thinner is to use a viscosity cup. A viscosity cup is shaped like a funnel and determines how thick a fluid is by the time it takes to empty the cup. A thin fluid will empty in just a couple of seconds, while a thick fluid might take 30 seconds or more. When I started spraying and used a viscosity cup, about 15 seconds was the right amount for my gun, but it will vary from gun to gun. When learning to spray, I recommend using a viscosity cup and to follow the manufacturers recommendations. If nothing else, this will give you a good starting point from which you can make later changes and have a way to achieve consistent results. After you spray for a while, there will be less mystery, and you will know from one test shot what needs to be adjusted, even without the viscosity cup.
When my customer asked about adding lacquer thinner, I know he was worried about possibly adding too much, and after thinking about it, I don’t know that you can add too much. I can follow the logic that adding too much thinner may change the chemistry, but I mix the 10:1 ratio of conversion varnish to catalyst first and then add the thinner, so there should still be the same amount of resin and catalyst, just with more space between them, in the form of lacquer thinner which will quickly evaporate and let the two parts do their thing. Even with other lacquer products, which includes sealers, nitrocellulose lacquers and modified lacquers, I can’t think of any time that I have ever had a problem because I added too much thinner.
I’m sure finish manufacturers would disagree and warn you to not be so cavalier about it, but I sure wouldn’t worry about adding too much thinner. Simply add enough thinner until your spray gun is able to apply a nice, even and wet film that flows out flat and dries without sagging. Even if you do mix it a bit thin, feel confident knowing that you can always compensate by moving more quickly or reducing the amount of fluid coming out of the tip of the gun.