TYPES OF HOLDDOWNS

[tommoser]

I seem to always be trying to figure out a better way to hold the material down on my cnc router.

Could a number of people respond and describe the ways they hold down work and if they have found a particularly good method.

Thanks,
Tom

[Perry]

Hi tommoser!
The method I typically use for the bulk of my signs is good old fashioned screws placed around the perimiter (which has been calculated a scrap). I have also used: cam locks I made myself, vacuum hold down table and on a two sided sign I do all my machining on one side, cutout the profile ith a 1/4" spiral cutter, flip the sign over, add 1/4" shims to hold in place. This is the same method I use to hold signs while I cut keyholes for mounting.
Hope this helps.

[dighsx]

Two words, carpet tape, for 90% of all the stuff I cut I use carpet tape and then I lock my clamps down around the work piece for insurance. I've used some normal two-sided tape for some small stuff but I've found the carpet tape works the best. Most of the time I have to use a screwdriver to get the piece unstuck from the table when I'm done.

Here's a shot of what I'm talking about. The block of wood is taped down and I just put the clamps there for insurance.

[rodm1954]

I use a lot of double sided tape. Also use sliding "F" clamps if the workpiece is close to the end of the table.

Jay- you must have beat me by seconds.

[RoutnAbout]

I also use doubled face carpet tape about 80% of the time and either use drywall screws with a squaredrive instead of the phillips drive ( the screw body it self is made different and usually harder to twist the heads off ). I usually don't use the tabbing with this method unless I can't be at the machine while cutting. I'm also reading and researching information for a vaccum hold down system.

Don

[Wemme]

Hello.
I mostly work from a complete sheet and use spring clamps to secure it to the bed and then use tabs to maintain positioning until done.
For Large slabs i use sliding "F" clamps then these tend to be so heavy the don't move anyway.
Regards
Bart

[Rcnewcomb]

Vacuum pods, shop vac, frame the piece with scrap wood, wood screws, 3M 90 spray adhesive, double-stick tape, clamps, anything but my hands!


10 fingers in, 10 fingers out -- another good day at the shop...

[Wemme]

Vacuum pods, shop vac, frame the piece with scrap wood, wood screws, 3M 90 spray adhesive, double-stick tape, clamps, anything but my hands!
10 fingers in, 10 fingers out -- another good day at the shop...

Hello
What sort of vacuum pump for the pods do you have?
Regards
Bart

[Rcnewcomb]

We bought pre-made vacuum pods from Nappy Products:
http://www.nappyproducts.com/vacuum_pod ... terial.htm

Now we buy scrap PVC or phenolic from a local outfit, drill two connected holes and apply some gasketing material from All-Star Adhesive: http://www.allstaradhesives.com/products.htm
and insert a vacuum hose connector.

Instructions about vacuum pods and such are available here (scroll down on the page once it loads):
http://www.baycraftdesigns.com/Shopbot.html

[Phil]

I read on the Shopbot forum once about someone using plastic decking material such as Trex to make pucks. I haven't tried it yet but I plan to.

[Wemme]

We bought pre-made vacuum pods from Nappy Products:

Instructions about vacuum pods and such are available here (scroll down on the page once it loads):
http://www.baycraftdesigns.com/Shopbot.html

Do you need a filter to stop dust and crap from ending up in the vacuum system?

[Rcnewcomb]

We put a filter in just in case some sawdust got sucked into the system. It seemed like cheap insurance.

[Mike Kelly]

About 5 years ago I put a little filter on a small vacuum pump I have been using for 15 years. Two weeks ago as I was installing my new ShopBot and de-comissioning my old homemade CNC machine I saw the filter and wondered how it (the vacuum pump) was still functioning. The front end of the filter was totally full. Pump still works fine. Filters are good, but check them every once in awhile. I used it intermittantly but obviously more than I thought!

[Ed Lang]

I use two Fein Turbo III's connected to a T and a 4 zone full bleed vacuum table for large sheets. I also use 1/2" Baltic Birch with All Star Gasket for smaller items that tend to not want to lay flat and move on the large vac table. With the center cut out of the 1/2" ply and gasket around the outside, just inside of the cut, I get super holding and quick cycle time between parts.

I also have a two stage high vacuum pump that I hold bowls on my wood lathe that is available to the CNC with pucks or pods. They also work super good. I have a square of Corian that I lay on the CNC and let the pucks stick to that. I still use my Turbo III's to hold the Corian down to the CNC.

I have not used a screw for a long time now. Nothing wrong with them! I am sure I will use them again.

Some jobs are run with a stop screws to the bed and I use two wedges against another stop. A light tap of the hammer and the wedges are tight.... another tap in the other direction, they are loose.

I am located at about 550' above sea level. Remember as you go up, you have less air to hold your parts down. I expect my setup would not work for someone in Denver, Co. for example.

I too am still looking for the magic bullet of hold downs but till that comes along, my two vacuum systems work real good for me.

Hope some of this helps.

Ed

[dighsx]

In another life I did work for a company that manufactured automotive parts. One thing they had that I always thought was neat was a magnetic holding system for automated milling. These huge blanks would ride along a conveyor and stop at different stations to get machined. At each station a rather large electromagnet would flip on and the part would lock in place in these clamps. These electromagnets were quite powerful, they tool a block of steel that had a warp in it and put it on and flipped the switch and you could see it bend it down.

One thing that occurred to me while standing next to these magnets is should I be worried about how close I should really get to these things. Like they might be limiting my chances of producing future generations if you know what I mean.