# An alternate work-holding method for my CRP-4848 CNC table



## Analias (Mar 17, 2014)

I'm curious about folks feedback on an idea I just had.

I have a CRP-4848 CNC table that I built.  The work area of the table is 48"x48", with the outside extents of the table being (approximately) 51"x60".  I have considered many options for work-holding on the table - vacuum, t-slots, 1"x1" hole pattern, etc.  At the moment I'm simply screwing the work down.  All of these methods require altering the table surface which would need to be replaced periodically.




I saw an article on Hack-a-day [1][2] for a work-holding idea that used two fix mounted carpenter clamps on a small CNC table.  This got me thinking about taking four steel bars, fixing two along the y-axis, and two movable along the x-axis and drilling/tapping all of them for 1/4-20 every 1/2".  To mount a piece for work, place it on the table and take the x-axis bars and place them "above" and "below" the work piece.  Secure the x-axis bars to the nearest y-axis holes, and then use smaller straps locally to finish holding down the work.

This avoids having to modify the waste board at all, and doesn't have to be redone every time you replace the waste board.  I would use 3/4"x1" bar stock, I tend to use 3/4" waste boards on my table, so the y-axis bars would be even with the rough table surface.

The only concern I can think of is how much flex would be exhibited on the x-axis bars?  Would it be enough to be a problem when milling hardwood, plastic, or aluminum?  The Y-axis would secured every 15" inches to the CNC frame, that shouldn't be a problem.

-Freeman

1. http://hackaday.com/2014/03/15/a-different-kind-of-cnc-workpiece-clamp/
2. http://dbugslife.blogspot.ca/2014/03/simple-cnc-clamp-workholding-system.html


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## xalky (Mar 17, 2014)

I'm trying to figure out how your plan is different from the links provided. The method in the links seems to be a good rigid method to hold down the work.


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## Thomas Paine (Mar 17, 2014)

you mean using drilling and tapping one of these so you can put clamps on top if necessary???:


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## Analias (Mar 17, 2014)

I was afraid I wasn't going to be able describe it adequately.  I may have to draw up a picture in Alibre to show what I'm considering.

Hopefully I can clarify it a bit more.  I wouldn't be using any slides or compression clamps.  The y-axis would be anchored to the outside of the table, perpendicular to each of the horizontal cross members of the frame.  The y-axis rails would be drilled and tapped 1/4-20 every 1/2 inch.  

The x-axis rails would also be drilled and tapped 1/4-20 every 1/2".  In normal use I would select a spot along the y-axis to bolt down the x-axis rails that would allow the work piece to sit between them on the table.  I would use smaller straps, bolted to the x-axis rail, to hold the work piece.

Hopefully I added to the clarity and didn't just repeat myself 

Modifying the saw rip guide is an interesting idea, but I would worry that the compression clamp would allow the rail to be positioned askew of the axis.  I'm trying to keep the inherit accuracy that I have designed into the table.  Drilling and tapping the 1/4-20 holes and paying some attention to the fit will help keep some that accuracy in the table when I need it.


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## xalky (Mar 17, 2014)

Like a soft nylon strap to hold  the piece down? I don't think that'll work at all.


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## bloomingtonmike (Mar 19, 2014)

You will need to surface your bed. Keep that in mind. Its why folks use MDF.


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