Easy Hold Down Table

discussion of design changes / improvements / suggestions
edwardrford
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Re: Easy Hold Down Table

Post by edwardrford » Thu Feb 07, 2013 4:19 am

@jzhvymetal: Those hold downs are AWESOME! I'm definitely cutting a set of those tomorrow.

-Edward
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alpha
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Re: Easy Hold Down Table

Post by alpha » Thu Feb 07, 2013 1:54 pm

I have a ShapeOko (2 Y stepper both with outside belt) with 20x20cm cutting area. I never cut a thing yet, but I'm planing to do that soon. Because I don't have any experiences in this regards I was wondering what would be a good grid spacing for the holes. I was thinking 5 cm (2 inch) would be good. This wound be a 5x5 holes and I would try to have more holes closer to the outside (like mirrored kind of logarithm around the center). Or I could imaged something like X and + overlaid (kind of like mill game, well this is a CNC mill so I guess this would make sense ;-)
Any other pattern ideas?
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TonyB
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Re: Easy Hold Down Table

Post by TonyB » Thu May 23, 2013 3:44 am

Just thought I'd bump this thread with some more pictures.

Image

I guess you could call this, a Shapeoko being 'self-sufficient'. Haha
Image

Image

Image

I haven't had a chance to do a test run, but it doesn't seem to want to move and I didn't even crank it down!

I'll be making some sort of bracket, but haven't made a decision on what I want to do yet. This thread has definitely helped expand on the idea.

Thanks!
Tony
MegaSquirted 62mm 7m @ 20psi on 91 octane
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PsyKo
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Re: Easy Hold Down Table

Post by PsyKo » Thu May 23, 2013 6:53 am

TonyB your idea is good. My experience told me that there is never enough fixation holes on the table. I think you'll probably need more holes, especially when dealing with smaller parts.

Nice Shapeoko though :)
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TonyB
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Re: Easy Hold Down Table

Post by TonyB » Thu May 23, 2013 1:20 pm

PsyKo wrote:TonyB your idea is good.
I don't know that I can claim it as my idea, haha. ;)
PsyKo wrote:My experience told me that there is never enough fixation holes on the table. I think you'll probably need more holes, especially when dealing with smaller parts.
I can totally see myself adding more.

As a developer my mind thinks in this order:
1. Is there a problem?
2. If yes to #1, fix the problem; if no to #1, fall out.
3. Test the fix.
4. Repeat.

When I was at True Value picking up bolts/t-nuts I wanted to have a whole every three inches, but roughly 25in x 25in ended up with a lot of holes! ((25/3)*(25/3) = 70'ish). So I grabbed 24 and told myself I'd figure it out and add more later if needed.

Right now it's 4 rows of 6; maybe I'll add another 3 rows (1 between each of the 4, if that makes sense) of 5, that way it makes for more variety.
PsyKo wrote:Nice Shapeoko though :)
Thanks! It's a work in progress. I just ordered the ACME Z Axis Upgrade and have had my eye on a dust shoe. My end goal is to be able to mill thin Aluminum (hoping 3/8-1/2 thick); I'm not sure if that's a pipe dream or not.

Anyhow, I hope the added pictures help inspire someone else to do this modification! Well worth it!
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PsyKo
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Re: Easy Hold Down Table

Post by PsyKo » Thu May 23, 2013 1:53 pm

TonyB wrote:My end goal is to be able to mill thin Aluminum (hoping 3/8-1/2 thick); I'm not sure if that's a pipe dream or not.
It's definitely not an impossible dream.
I'm able to mill 10mm aluminium on my Shapeoko.

Actually the clamp you can see on the 3rd picture of this post http://www.shapeoko.com/forum/viewtopic.php?f=30&t=1608 has been milled using my unmodified shapeoko.
I've milled another one and it's pretty good.
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WillAdams
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Re: Easy Hold Down Table

Post by WillAdams » Thu May 23, 2013 1:58 pm

Spacing the holes is an interesting problem.

I think a better thing would be to use some sort of ratio, say a doubling / halving. In retrospect, for my 1 meter Y-axis upgrade I wish I'd standardized on 36" and done pairs of holes at something like:

36"(+1) and 0" (-1) (to define the beginning and end)
18" (middle)
9" (for smaller projects)
4.5" (tiny)

This would let one clamp down things which are:

36" (full run)
27" (36" and 9" holes)
18" (36 and 18 or 18 and 0)
13.5" (14 and 4.5)
9" (18 and 9 or 9 and 0)
4.5" (9 and 4.5 or 4.5 and 0)

But, looking at those numbers, some other proportion would probably be more flexible --- I guess this is another argument for phi / golden section.

Heck, I managed to mangle my own layout by switching from an Irwin side vise to a Bessey --- did this after my table was all glued together and the spacing is closer on the Bessey side clamp and I stupidly put the holes I'd planned to use for the Irwin as far apart as possible.

I really like alpha's layout --- wish my machine were wider so that an elegant arrangement like that would make sense for me.

William
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cvoinescu
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Re: Easy Hold Down Table

Post by cvoinescu » Thu May 23, 2013 6:37 pm

How about making a smaller board with dense holes, which you can secure into the wider-spaced holes in the bed when you need to clamp something small? It also has the advantage of raising the work surface a little, which means slightly less deflection. For a specific job, you can clamp a blank piece of plywood and mill a fixture -- basically, a pocket to hold your workpiece.

What I've learned from the little DIY carpentry I did around the house, before I got into CNC, is that it's often worth spending the time to make a jig. It's worth spending an hour to make a jig and five minutes to do the job, rather than spend an hour doing the same job, only less well, with hand tools and no jig. If you then need to do the same job again (e.g. hang a door), all that saved time is just gravy. I have a crate in the garage with router jigs for hinges and door latches. Just yesterday, a friend asked me to help them hang a door. Guess what job is going to be done in half an hour flat. :)
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WillAdams
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Re: Easy Hold Down Table

Post by WillAdams » Thu May 23, 2013 6:52 pm

Agree on the jigs aspect.

I'm a little saddened by the ``raising the work surface'' == slightly less deflection, since I went out of my way to raise my machine up so as to increase my Z-axis room though.
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Improbable Construct
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Re: Easy Hold Down Table

Post by Improbable Construct » Thu May 23, 2013 7:22 pm

WillAdams wrote:Agree on the jigs aspect.

I'm a little saddened by the ``raising the work surface'' == slightly less deflection, since I went out of my way to raise my machine up so as to increase my Z-axis room though.
Its all about the lever. The closer the bit is to the X axis gantry, the less the lever can flex the X to Y transition.
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