How to hold pieces down on a CNC machine?

[twisted8]

Hello,
I haven't had much luck cutting good pieces with my cnc machine. I'm using double sided tape and usually the pieces end up moving anyway and get messed up. Another problem is that sometimes the router gets stock on the double sided tape while is cutting and it makes it skip.

Any suggestions?

thanks

[Polmer]

I bolted a piece of plywood on the main CNC deck.
I then screw the piece to be cut into the plywood so it cant move.

~Polmer

[mondo50m]

I sometimes use a piece of self adhesive shelf paper on the bottom of the piece to be cut, after attaching the shelf paper, I spray it with 3M spray adhesive and attach the material to my sacrificial base piece. This keeps the spray adhesive off my piece and eliminates alot of cleanup.

Milt

[Hessel Oosten]

Examples:

http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/P1140004.JPG
http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/P1120279.JPG
http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/P1120281.JPG
http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/P1120276.JPG
http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/P1080227.JPG

The T nut table is not obligatory of course.
Many people make holes in a thick plate of mdf/plywood where nuts can hammered (right word ?) in.
These nuts have screw thread inside.
http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/7965.png
In this thread you can screw a bold for holding the clamps.
Clamps can be milled on your own mill.
Mills making parts of mills !

Hope this helps.

Hessel

[mefiu]

Forget the tape. Tape is good only for PCB isolation milling.
Use T-table (which is expensive) or use these http://radiomodels.com.pl/images/nakretka-klowa-m5.jpg at the bottom side of your MDF or playwood table. Glue them to the table using epoxy glue or something like that.
These http://www.elektor.nl/StreamFile.lyn...Posts/7965.png (http://www.elektor.nl/StreamFile.lynkx?path=Uploads/Forum/Posts/7965.png) are not good enough IMO - could be easily twisted while mounting your object to the table.

[Westozy]

I have 16mm MDF fixed to my table and I use aluminium 'bridges' with a wood screw. Place some spacer material that is the same thickness next to the work piece then drill a small hole into the sacrificial MDF table between the pieces. The aluminium bridges are 3mm thick with a hole in the centre, the screw down the bridge trapping the work piece and the spacer piece. I also use 'hook' bridges which are L shaped and made for specific thickness materials as seen in this picture -
http://www.mycockpit.org/photopost/data/560/04-Making-footplate.jpg
This rudder pedal part is being machine from a piece that used to be the side of my console structure - recycling the Boeing!
Cheers, Gwyn

[twisted8]

thanks guys! great suggestions! gotta give this a try.

How would you hold small pieces tho? for example i'm trying to cut small acrylic blocks for annunciators but they seem to fly away right before the router finish cutting. Maybe I need to use a smaller bit? i'm using 1/8" (3 mm) so it creates a pretty big space between the small piece being cut and the main piece.
Thanks

[Wendy]

You could use "bridges", these are for example 4 small bridges of material that the router does not cut away when the part is cut out. The toolpath software normally has the possibility to define "bridges".

Regards, Wendy

[Perik]

Hello twisted8

For your last "problem" try to not mill all the way through the material - just
leave a few 1/10 mm. Then you can either break the pieces out or use a knife
and finish off by filing and sanding.
A second way is to flip the working piece and mill of from the backside.

http://www.hoddo.net/images/cockpit/glare/20-korry-1-s.jpg

This picture show my MCP Korrys (though in MDF - more or less the same for Acrylic)
from the top side and as you see my top knob surface is a approx. 1mm lower then
the top surface of the workpiece so when you flip and mill from the backside
and the knob / Korry is released it will "fall down" and does not come in conflict
with the milling tool.
Some cleanup afterwards is nessasary in any case.

Happy milling.

[wannabeaflyer]

Hi Guy my mk one CNC is finished and cutting bits like mad at the moment --mayerial of choice Delrin :-) my machne may not be the Prettiest on the Block but she cuts great and is repeatable - so much so she is making all her own upgrades, and bits for a 2nd machine designed for PCB Routing and smaller precision light cuts parts :-) will post some pics later and take a look at my Youtube clips when i publish the link in my next post...anyways i tend to now place screw holes in Non machined zones an screw tha part down with wood screws to a sacrificial Board, i have had good success with this method. for my CAM i use Vectric 2d for Producing my G code, i have to say bang for bucks im very happy with that piece of software as it allows my to put Holdown tabs around the Job to stop it from flying out when it finishes the last cut .. i know that's all been mentioned already but just so excited that my machine is up and running at last. look forward to contibuting my nutty professor ideas and designs to this forum Cheers Guys and Gals

http://www.youtube.com/watch?v=0iK1jiyvGho

Also added Pictures to my album page :-)

[wannabeaflyer]

Hi Guys tis only mee again some pics of my prototype CNC router ( i use that term very loosely ) ok ok i'll settle for Lash up but ii point out and accurate and effective Lash up LOL :-)
https://picasaweb.google.com/wannabeaflyer/Pics#5564729732172807810

[twisted8]

thanks again for all he advice! i have seen the option to make the bridges in the software I use but I've never tried it. I will try that. :)