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Discussion Starter · #1 ·
as we get closer to our fist cnc (turnkey) purchase, I have been considering the needs for clamping the work down. we will be small run production and one offs. vacuum seems overkill, but definitely see time advantages.

what do most of you use? any clever tips? thanks in advance.
 

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Oliver (Prof. Henry)
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Here's my solution for clamping standard sized blanks for easily making multiple copies of a project. It uses positioning brackets and cam clamps that attach to the spoil board. Still waiting on delivery of some baltic birch ply for the clamps so all I have is this V Carve layout representation at the moment.
 

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First I took the factory MDF bed and routed out some dado slots and added T-track from Rockler


Then I got some T-slot from 80/20 and replaced the MDF bed



You can buy aluminum clamps from Rockler or cut your own from hardwood scraps. This works best if you have other than "standard" needs.

Just drill a hole and slip a carriage bolt in the track, put the clamp on the bolt, and tighten it with a threaded knob or a plain old nut.
 
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Tim Clement, a local custom chairmaker, uses vacuum clamping on his large CNC setup. He's routed a grid of channels into his spoilboard, lays out an appropriate 'circle' of round profiled 'O' ring cord material*...closed loop obviously...then lays his material to be carved on top. Turns on the vacuum and away he goes.

*https://www.jameswalker.biz/en/products/279-o-ring-cord

Like this...
 

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If you are doing a production run of identical parts then reference ledges plus cams or wedges like Gaffboat shows above will probably be your best bet. You don't need t-track or threaded inserts or vacuum, but can simply screw down the ledges and cam or wedge backer block. If you have room on your bed for more than one unique part you can jig them all up, and use different coordinate systems with each to not even have to set your X/Y/Z origins between cut sessions or days.

You can make ledges that have a slightly sloped overhang to also hold down the parts while they are being cut.

4D
 

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Here's my solution for clamping standard sized blanks for easily making multiple copies of a project. It uses positioning brackets and cam clamps that attach to the spoil board. Still waiting on delivery of some baltic birch ply for the clamps so all I have is this V Carve layout representation at the moment.
Dang Oliver, those positioning brackets look almost identical to what I am using...and they work well.

Saying that, I used a 60 deg v groove bit and created a file for the CNC to cut a very shallow groove 2 inches in from the outside of the spoil board and at 90 degs also - 18 inches both ways. Then I attached the brackets accordingly.
 

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Mike
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Just remember that if you are using upcut spiral bit they are made for lifting chips from your cuts and they don't know the difference between a chip and your material.

As 4D said "You can make ledges that have a slightly sloped overhang to also hold down the parts while they are being cut." You can also do this to cam clamps.

Vacuum tables are great for face carving but not so good for cutouts unless the vac clamp is designed for the project so that the bit will not be cutting through the seals. Used correctly they can save a lot of time.
 
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Discussion Starter · #8 ·
psuedo - home

my previous career dealt a lot with mechanical positioning, and we always had an X - Y home at the upper left corner. in your posts I have been noticing that maybe a "job" home position may be assigned, e.g. where the work is clamped. maybe called a job offset in relation to the x-y position of the clamped work piece?

is this typically a corner of the work piece? center?

and then obviously the tool paths need to miss all of the clamps to get there? do you retract full y or just enough to clear?

sorry I have lots of questions...
 

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honesttjohn,

Would you mind telling me what brand and size your C N C is? We have a small unit now and thinking of upgrading to a larger machine. Any help or thoughts along this line would be appreciate.

Thanks,

Tagwatts1
 

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The Nebula bed area is 37" x 50", with 5" of Z travel although only roughly 3" is available above the MDF bed.

We also have a Nebula in our college furniture design shop. It sits next to our Meteor from the same company. The longer gantry has more flex when challenging the router/spindle with deep profile cuts in hardwoods. There is vibration that happens. More when the router is in the middle of the gantry, and when making cuts that move in the Y direction. Fine for most work, but I've pretty much stopped using it for such cuts that could be done on our Meteor instead.

4D
 

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honesttjohn,

Would you mind telling me what brand and size your C N C is? We have a small unit now and thinking of upgrading to a larger machine. Any help or thoughts along this line would be appreciate.

Thanks,

Tagwatts1
Frank,

Probotix Nebula. I put a couple cross members in to help stabilize the bed. With that being said - I could have gotten away with the Meteor for what I've done ......so far. That will probably be my second machine unless I do something really stupid and decide to get serious about all this.
 
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