twforeman's Shapeoko 3 #0004 Upgrades - Long

chamnit
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by chamnit » Thu Jan 21, 2016 11:45 pm

Love this thread. Thanks for sharing your progress/experiment.

I'm surprised that there was so much of a clear hump in the middle of your table. It seems odd and it's likely that it might be a product of the pocket hole screws. Torsion tables are really sensitive to assembly error, and the stresses involved with fastening the ribs tightly could have knocked your table out of alignment. Gluing and using a brad nailer might be less invasive, but the nails would swell the Mdf around the nailing site. Whatever you do I'm not sure you can completely get rid of assembly error.

Maybe the solution is to use less ribs, particularly the crossing ones. Or just assume the final table will have some error and correct for it afterwards. The latter seems to be the better option, if there is a way to do it easily. Like using a straight edge and sanding down high spots, but doesn't help with making sure the top isn't twisted.

Very curious what you end up doing!

EDIT: Ah. I noticed the two 2x4 support rails. Did the table end up sagging between them?

twforeman
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Fri Jan 22, 2016 2:16 am

chamnit wrote:Love this thread. Thanks for sharing your progress/experiment.

I'm surprised that there was so much of a clear hump in the middle of your table. It seems odd and it's likely that it might be a product of the pocket hole screws. Torsion tables are really sensitive to assembly error, and the stresses involved with fastening the ribs tightly could have knocked your table out of alignment. Gluing and using a brad nailer might be less invasive, but the nails would swell the Mdf around the nailing site. Whatever you do I'm not sure you can completely get rid of assembly error.

Maybe the solution is to use less ribs, particularly the crossing ones. Or just assume the final table will have some error and correct for it afterwards. The latter seems to be the better option, if there is a way to do it easily. Like using a straight edge and sanding down high spots, but doesn't help with making sure the top isn't twisted.

Very curious what you end up doing!

EDIT: Ah. I noticed the two 2x4 support rails. Did the table end up sagging between them?
Yes, I'm pretty sure the error was caused by the sag between the supports.

I'm not sold on the pocket screws either. I may just clamp glue and brad nail the next one. Still thinking on it.

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by LTEPM » Fri Jan 22, 2016 3:12 am

twforeman wrote:
FargoPhil wrote:How much do you expect the table to move due to humidity changes? .03" is way flatter than I'd expect to achieve by any means, especially from MDF.
I don't know, but I don't expect it to move very much. .030" is a pretty large flatness variation - 1/32 of an inch. I'd like to stay under .010" or less. I don't think there is any reason I can't approach that level of accuracy.

I'll build another one and see. I also don't have a really good straightedge to measure with but once I bolt the Shapeoko to the table I can run a test indicator over the table and see what kind of variation I get.
If you have a low angle plane you can plane the MDF. Marhthe high area and plane it down. You can use a block of MDF with sandpaper to do your final flattening or a granite plate with sandpaper glued on.

It's really not that much to take off, how large of area is it not flat?

As a general rule I stay away from pocket screws on torsion boxes, use half lap joints on the ribs, and staple the faces. Your table saw likely has the largest flat surface in your shop.

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Fri Jan 22, 2016 1:54 pm

LTEPM wrote:If you have a low angle plane you can plane the MDF. Marhthe high area and plane it down. You can use a block of MDF with sandpaper to do your final flattening or a granite plate with sandpaper glued on.

It's really not that much to take off, how large of area is it not flat?

As a general rule I stay away from pocket screws on torsion boxes, use half lap joints on the ribs, and staple the faces. Your table saw likely has the largest flat surface in your shop.
I thought about planing it down, and I may give that a shot before building a new one. The whole middle of the surface is bowed up - most likely due to sag between the supports during assembly.

Lap joints are a bit more work than I think are required for a torsion box.

My saw is actually not very flat. It has a hump in the middle. It doesn't really cause much issue in use, but as an assembly table for making flat things, it's not so great.
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by LTEPM » Fri Jan 22, 2016 2:09 pm

If you decide to hand plane the MDF use a low angle plane if possible and keep your blade sharp.

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Fri Jan 22, 2016 3:20 pm

LTEPM wrote:If you decide to hand plane the MDF use a low angle plane if possible and keep your blade sharp.
My only low angle plane is a small block plane. Probably not the best for flattening large surfaces... :cry:
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WillAdams
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by WillAdams » Fri Jan 22, 2016 3:26 pm

Look at this as a chance to buy a new tool.

I got lucky and picked up all of my planes off Craigslist or eBay, but Lee Valley, Lie-Nielsen and Bridge City Toolworks all make fabulous ones.

When I was a kid though, I'd use my father's old Stanley block plane on even large boards, since it was all I had, unless I went into town and worked in Meriwether Smith's shop (his wife was my Great Aunt Annie Mae's bridge partner) --- wish I knew what happened to it (also sad about what happened to Mr. Smith's shop).
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twforeman
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Sat Jan 23, 2016 7:40 pm

So there is good news... I did use this as a chance to buy a new tool but what I bought was a 48" level with milled sides. Guaranteed to be flat to .0005" (right, pull the other one, it's got bells on.)

In any case it's bound to be straighter than my extruded aluminum circular saw guide.

The new level indicates that my torsion table is pretty darned flat!

This makes me happy and now I can continue with the build.

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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by twforeman » Sat Jan 23, 2016 11:43 pm

In more good news I took apart the Shapeoko 3 base, popped out the pressed in nuts, drilled out the holes to 5/16" and checked the T-Nut positioning...

They are just about dead-on in all three positions. I'll probably open up the holes in the end pieces another 1/32" just to give me a little more wiggle room for alignment, but I'm feeling pretty good about this project now. :)
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sjj47
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Re: twforeman's Shapeoko 3 #0004 Upgrades - Long

Post by sjj47 » Wed Jan 27, 2016 12:59 am

This is a great thread - very informative. Since I've rebuilt my table a few times I find it very interesting.

One (perhaps dumb) question. Why the torsion box? I know a lot of people use them, and I've built them myself before, but only for heavy tools. The S3 isn't that heavy. I've gotten away with two layers of 3/4" MDF with no obvious problems. And the S3 steel base is only supported at - what - 9 points on rubber feet?

If it is a question of flatness, wouldn't tramming the actual wasteboard surface handle that?
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