Precision or really.. lack of precision

A discussion about the second version of the Jointmaker Pro

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Precision or really.. lack of precision

Postby paul@paulkirchnerstudios.com » Wed Feb 15, 2012 3:13 pm

I got my Jointmaker this last round of manufacturing. It went together smoothly but I struggled mightily to achieve a repeatable 90 degree cut. And that is 90 degree from the blade to table. I'd get close and put the flip stop against it and then move the keel out of the way and put a thin spacer (in my case a Bart rapid transit card which is a plastic that mikes out to .007) and move the keel back in place...yes by holding it in the middle when moving it. And go through the whole tedious allen wrench alignment of front and back.

Make another cut. Most of the time it resulted in the exact same cut as before. Go through the whole process and then the cut is off the other side.

When I did hit 90 a raised fist and a little dance resulted, and I would try another cut and most of the time it wouldn't be 90 anymore. On the same piece of wood a little away to get rid of that variable, and all the other things necessary to try and maintain a rigid approach...Same number of cranks in between, the same amount of force of the push, and of course a system that would not allow any wood movement.

Anyway, I gave up and used the saw on some inlay cutting where the depth of cut was only 1/8" or so carried on. A couple weeks worth of cutting.

Now I'm starting another project and all I want to do is to cut a perfect 90 degree with a miter. The stock I will be using will be 1/4" X 1"

I can hit it on similar size pieces of cherry and soft maple most of the time but the real stock, which is jarrah, the last part of the cut veers off.

I have aligned and realigned using John's allen wrench method. I have used the dial indicator method. I have replaced blades. And then I do it all over again. The table runs perfectly parallel with the blade. I have tried small pitch cuts and big pitch cuts.

Attached are a few pics. This is after a cut and I removed one side of the wood but left the other side exactly as it was cut. The beginning of the cut and blade to wood looks good. The end of the cut and you can see how the wood veers off. And the old light shining through with a square on top photo.


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Re: Precision or really.. lack of precision

Postby John@bridgecitytools.com » Tue Feb 21, 2012 11:31 am

Paul-

Couple of things can cause what you are experiencing.

1) Make sure that the fence your stock is resting against has a kerf larger than the blade--this is really important. In other words, as the blade exits your stock, you don't want it touching any part of the fence. In the early days I thought a "zero clearance" fence was a great idea and it is not.

2) Double check that the blade is indeed parallel to the table travel. I have three saws I use, and once I dial in 90 degrees, I set flip stops on the same side of both the front and rear plates. Because most people assemble their units, this technique removes any variables in the trunion fit. It is possible with trunions that are too tight to adjust the keel and the blade is no longer parallel to the table travel. When this happens the blade literally bends during the cut creating a crooked (and often repeatable) cut. For mission critical cuts, I almost always double check blade alignment with my pocket rule--it takes just seconds.

3) Make sure your blade guides are not causing the issue. Here is a way to dial them in dead on;
Take both tables off. Raise the blade as high as it will go. Loosen the blade guides and slowly slide the BLACK guide until it kisses the blade fore and aft and tighten. Now pinch the other blade guide and tighten. Re-attach both tables.

4) This is rare but I have seen it a couple of times; with the blade raised, lay a straight edge on your table and see if the blade is indeed straight. If not, the blade guides need to be replaced.

5) Once you have confirmed all of the above, make your cut with a new blade (dull blades cause all kinds of accuracy grief).

6) I am assuming you are using the standard cross-cut blade. Our thin blade is awesome for really small cuts (architectural models, jewelry, etc) but will not track straight in thicker material as the blade will follow density changes in the stock.

Lastly, and this is probably not the case, but cutting should feel almost effortless. When you can feel the blade fighting back, take more passes with a lighter bite.

If you can make consistent inaccurate cuts, then we can make consistent accurate cuts--just have to track down the culprit.

If you are still experiencing this issue, I want to pick up your saw and work on it here.

-John
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Re: Precision or really.. lack of precision

Postby paul@paulkirchnerstudios.com » Tue Feb 21, 2012 4:30 pm

Thanks for the suggestions John,
#1. I read somewhere you writing about the zero clearance fence often throwing off the cut so I don't do that when adjusting the cut.
#2. I triple and quadruple check that the table runs parallel.
#3. Can't do that right now. I gave up on trying to get a good cut with the blade at 90 degrees to the table and went with the blade tilted to 45. I cut hundreds of little pieces of wood and now have the saw all dialed in to cut the second part on each piece and don't want to undial it right now... See attached photo
#4 I did indeed had a very not straight blade when I first put the saw together...see my discussion about it here...
viewtopic.php?f=22&t=291
#5 I was using a brand new blade on the above photos.
#6. I suspected that as well, that maybe I was shipped with the thinner blade but not the case. Am cutting with the standard blade.

After I finish up with what I am doing with the saw with this project I am going to tear it apart (somewhat) and rebuild it.
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Re: Precision or really.. lack of precision

Postby John@bridgecitytools.com » Tue Feb 21, 2012 4:47 pm

Paul-

OK-let's see how it goes after you get done cutting miters--I know it is solvable.

Cool image BTW--do you count miters in your sleep?

--John
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Re: Precision or really.. lack of precision

Postby paul@paulkirchnerstudios.com » Tue Feb 21, 2012 5:00 pm

Let's say it's occupying my thinking process right now. You ever asked yourself halfway through something why you started it in the first place?
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Re: Precision or really.. lack of precision

Postby PFranks » Sat Feb 25, 2012 11:40 pm

Man, Paul: I can hardly wait to see what you're making! That's a lot of little boxes...
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Re: Precision or really.. lack of precision

Postby paul@paulkirchnerstudios.com » Mon Feb 27, 2012 12:52 pm

Peter,
Just about this time last year I was drinking Sherry in Jerez da la Frontera, Espana and struck up a conversation with a Japanese businessman at the bar. What he said directly led me to this project, something I'm doing for my daughter sandwiched between/within a couple paying gigs.
But last week I emailed her saying I didn't know if I had the giddy up to pull it off since I couldn't hold tolerances from the JointMaker. It's been one chase after another trying to keep things consistent on a long production run like this. I'm thinking I'm going to dedicate a separate thread to this. So I'd rather not reveal everything in case I give up on the whole project.

The miters are not really for boxes per se; eventually they will become a square though.

Some pics.
A portion of the pieces with half laps cut.
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Before they become square, they must become a triangle.
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Then they can be arranged into their final forms. The only way I think this will work is if I rework each triangle to bring them back into tolerance. Wish me luck.
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Re: Precision or really.. lack of precision

Postby papinc@aol.com » Thu Jan 31, 2013 9:49 am

for those of you wishing for precision, i see that john's masw "precision unparalleled" class was sold out in record time. there was such a wait list that john and marc agreed to add another precision unparalleled class in the fall. so, for any of you who were left out, call masw to get in the fall class. go john!
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