My latest jig build - this one is special

[Ola Carmonius]

@Jay I beleive you could also print the 2d drawings on A2 paper and use directly as template. Most drawings are done on A3 sheet in scale 1:2. I had ideas to make the drawings in scale 1:1 A2 format but not many have possibility to print that big.

Must be tough to have a different unit system than the rest of the world You will need to master the mm system anyway when you start using the jig.

[Wes Grass]

If you really want it in inches, ballscrews are available in 4 or 5 TPI. Not likely to find them cheap though. I checked McMaster, the screw isn't *too bad*, but the nut and supports ....

Another option is to drive the metric screw with a 47/37 tooth gear set. 4mm = .20", 5mm = .250". The ratio is accurate to the 5th decimal, significantly better than a rolled screw itself. It'll be 'backwards', and you'll have some bit of backlash in the gears, but there may a little bit in the screw/nut anyway. Just keep going in one direction til you're done.

47/37 is a 'cheap' way of cutting metric threads on a lathe with an inch leadscrew. Exact requires a 127/100 combo. Not easy to mount up on a typical lathe, and harder to source.

[Jay Houghton]

If you really want it in inches, ballscrews are available in 4 or 5 TPI. Not likely to find them cheap though. I checked McMaster, the screw isn't *too bad*, but the nut and supports ....

Another option is to drive the metric screw with a 47/37 tooth gear set. 4mm = .20", 5mm = .250". The ratio is accurate to the 5th decimal, significantly better than a rolled screw itself. It'll be 'backwards', and you'll have some bit of backlash in the gears, but there may a little bit in the screw/nut anyway. Just keep going in one direction til you're done.

47/37 is a 'cheap' way of cutting metric threads on a lathe with an inch leadscrew. Exact requires a 127/100 combo. Not easy to mount up on a typical lathe, and harder to source.

My feeling about joinery in woodworking is that it's not metal working. You can't get machining down to the same levels as metal because the next day that fresh surface you just machined will be bigger or smaller depending on the humidity in the shop and the moisture content of the wood. Also, there has to be room for glue, which the vast majority of is water based. As soon as you start the glue up you're on the clock, not just from the glue drying out but of it expanding the joint to a point where it no longer fits together. A piston fit is a thing of beauty but not practical for woodworking. (IMHO of course).
Jay

[Jay Houghton]

Good morning Ola...working my way through the build. Mainly assembling all the parts I need so I haven't started cutting anything yet!


I saw that your "go to" blade is a 6mm FTG rip blade, and since it's orange I presume it's a CMT brand. That sounds like a great idea. I cannot find that blade in the catalog however, do you have a model number for it? What they do sell is a two-blade set where you reverse them to get a 3/8" width. So you're buying two blades essentially. They really are made for the Incra box joint jig you can buy and people that make jewelry boxes like the small kerf.

Anyway, I'll post progress photos as I have them.
Jay

[Ola Carmonius]

Well, that CMT blade is not my go to blade anymore. Thought it cut a bit sluggish and I didn't really like the cutting feeling. Checked it in detail and the tops were not really flat, they were all leaning in one direction and I guessed that effected the feel. That is manufacturer error and I will have it regrinded and give it a new try. Waiting for that to happen, I have switched to a 4mm flat top rip cut blade. Cuts much better than the CMT one. The new blade is from a local Swedish blade manufacturer so won't be of much help. Photos attached.

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[Wes Grass]

My feeling about joinery in woodworking is that it's not metal working. You can't get machining down to the same levels as metal because the next day that fresh surface you just machined will be bigger or smaller depending on the humidity in the shop and the moisture content of the wood. Also, there has to be room for glue, which the vast majority of is water based. As soon as you start the glue up you're on the clock, not just from the glue drying out but of it expanding the joint to a point where it no longer fits together. A piston fit is a thing of beauty but not practical for woodworking. (IMHO of course).
Jay

I totally agree. I've made that mistake a number of times. I made wooden screws for a Moxon, threadmilled them on the lathe with an endmill in a toolpost grinder. They fit great, for awhile ... one will probably require a pipe wrench to get out.

As for inch vs metric, there's always going to be some level of calculating anyway when you consider the blade thickness and glue allowance.

What I like about a screw driven jig is that it's 'absolute', rather than a series of incremental movements off a stop pin where error adds.

[Ola Carmonius]

I agree with you both and I think I mention that in one of the usage videos. The important thing is not if I cut a tenon to exactly 12.00mm, its rather that if I aim for 12.00 thig jig will be consistent and keep it within a few 0.01mm from the target, on all tenons. Second and maybe most important thing is the pin system enables predictable trims in steps of 0.05mm. The actual dimensions of wood is really not that important, it's the fit between the parts that matters, and it's really easy to fine tune that with this jig.

[Jay Houghton]

I'm making progress on my jig build. Only a few adjustments for using 18mm plywood. I've learned a few tricks along the way, especially about getting cross dowels to fit right, which is, don't think you can drill that kind of precision on a drill press. You need a CNC! However I used a slightly larger diameter drill for the screw holes and that allowed enough wiggle room to catch the threads of the cross dowel. All the rest of the dimensions were spot on so just build to the specs and the overall design will come together. I'm in the final stages and decided not to install a DRO, and I'm having a friend machine the three components of the hand wheel on his CNC, including engraving the markings and drilling the 80 holes! Huge savings of time and effort. I'll report back once I get them from him. I'm also going to use T-track on the carriage instead of routing a dovetail way, or T-track channel since I have the T-track already.

My cost on this is in the $150 range partly because on some of the components like the flange coupling, cap screws and the like you have to buy way more than you need in order to get the price down. I also paid FedEx/Kinko's to print about 15 drawings at $2.25 per page so I could see them closer to actual size.

All in all I'm excited about the jig. The precision of 4mm/80 resolution should be a nice step up from the usual way of making finger joints. Not counting the labor, to get this for less than the cost of an I-Box jig is not something to discount.

JayBall screw and rails.jpgCarriage.jpg

[Ola Carmonius]

I'm making progress on my jig build. Only a few adjustments for using 18mm plywood. I've learned a few tricks along the way, especially about getting cross dowels to fit right, which is, don't think you can drill that kind of precision on a drill press. You need a CNC! However I used a slightly larger diameter drill for the screw holes and that allowed enough wiggle room to catch the threads of the cross dowel. All the rest of the dimensions were spot on so just build to the specs and the overall design will come together.

No CNC needed, the solution is just as you did to drill the screw holes in both pieces slightly bigger than nominal. All cross dowel screw holes are oversized in the plans, but if you swapped metric for imperial screws that might not be so obvious.

[Jay Houghton]

I'm almost done, I was going to skip the DRO but decided it would be useful so I ordered one. I did encounter an unanticipated problem, which is that I though it would be no problem to use a Freud box joint jig (1/4 or 3/8") on a metric device. Well, it isn't! There's just way too much math involved in getting a 3/8" finger to fit in the other side. So my solution, since you can't buy a metric box joint blade, was to put a 0.0190" shim from my dado set between the two blades, and now I have a 10.007mm kerf on the blade. My fist sample was too tight but with the resolution being .05mm you can simply move the carriage a couple holes to adjust the fit without creating any cumulative error since your reference for the next cut is always the Zero point on the part, not the previous cut. The other advantage is that you can cut multiple parts at the same time, like (4)-1/2" pieces at once.
Jay

[Ola Carmonius]

Hi Jay,

As mentioned, if the blade is imperial or metric thickness is of no importance. Boxjoints are cut in metric numbers (very important) and control wheel indexes metric no matter if the blade is metric or imperial. 3/8" blade equals 9.525mm and can be used for 10mm boxjoints and bigger with just as good results as using a 10.00 or 10.07 blade. None of the blades though can be used for cutting imperial boxjoints on this jig. So, think metric and cut metric boxjoints and use any blade you want, imperial or metric.

Example: 12mm boxjoints. With 9.525 (3/8") blade, measure the sawed kerf, let's say it's 9.55. Put the green pin in the zero, red pin in 2.45 (12-9.55).

With 10.07 blade, measured kerf is maybe 10.1. Green pin in the zero, red pin in 1.9 (12-10.1).

Kerf effects red pin position but nothing else. When cutting mating piece, move carriage one finger thickness, 12mm. In this case that's three whole turns on the control wheel so no reason to move the pins. Move the notes to equal the new zero position, cut the mating piece. Also this operation is totally independent of the saw blade thickness.

[Wes Grass]

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Eyeball alignment should be good enough, but you still need a decent chuck.

[Ola Carmonius]

Jays talk about varying finger widths inspired/challanged me to try out some patterns and varying finger widths the latest days. If you are into these kind of joints with variations this jig will give so many options, these I show here are just a few examples. Once familiar with the system irregular patterns or not complicated at all. All joints done with my 3.2mm flat top blade. None of these joints are glued or sanded, this is the dry fit accuracy acchieved with this jig.

First picture finger widths only 4mm on the "non visible side" of for instance a drawer. Fingers on visible/front goes in a decreasing-increasing series 20/16/12/8/12/16/20.
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Half of that series looks like this, maybe a bit more clean look.
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Next pic both fingers goes in a series of 16/14/12/10/8/6/4 and in the opposite direction to each other. From the top mahogny goes to thicker fingers, ash to thinner. They meet halfway. Takes a while to see it maybe.
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Final pics just to show how versatile this is also for larger joints like this bridle joint in 59x59 dimension wood. With only 5 fingers no evenly divides numbers are needed, with 6 colour pins finger widths can be whatever they need to. In this case my piece of wood was 59mm and the fingers ended up at 59/5=11.8mm. Control wheel set up for this joint also shown. Here the fingers are planed flush, would be to good looking otherwise. Not glued though.
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