Vacuum holddown pump

[toddmaci]

I am looking to make a vacuum holddown jig to cut maple items. Would a Robinair, model 15600,6cfm,1/2 hp work.
http://cgi.ebay.com/Robinair-SPX-Cooltech-Vacuum-Pump-15600_W0QQitemZ400069991616QQcmdZViewItemQQptZLH_D efaultDomain_0?hash=item5d26079cc0&_trksid=p3286.c 0.m14

Thanks,

Todd

[Gary Campbell]

Todd...
That should work if you make a gasketed fixture that does not leak. These high vac, low cfm pumps do not work with a spoilboard.
Gary

[toddmaci]

Thanks Gary, I am planning on making a dedicated jig for this.

Todd

[toddmaci]

Gary,
Would you recommend one of these? Do I need anything else besides the pump and this kit and HDPE?
http://www.joewoodworker.com/veneering/vacuumclamping.htm

Thanks,

Todd

[Gary Campbell]

Todd...
That kit should have what you need. The foot valve is not the cheapest solution, but they do work well.
Gary

[toddmaci]

Gary,
Do you have a cheaper solution you could recommend?

Thanks,
Todd

[Gary Campbell]

Todd...
Any 3 way valve with fittings to your tubing will work. The line to the fixture goes to the common port, then 1 of the others to the pump and the last to atmosphere to allow the fixture to release.
Gary

[toddmaci]

Gary,
Simple,cheap and elegant. Do you think I need a filter?

[Gary Campbell]

Todd...
Yes, a filter can protect your job from damage.
Gary

[cnc_works]

In my experience, I really wouldn't recommend this automotive style pump, it has a bad tendency to put an oil mist into the air. Early on in my cnc work I tried more than one of these and found it an unpleasant companion in the shop. I think You are much better off with a carbon vane pump of some sort. Watch Craigslist, check local surplus and you should find something better suited.

Donn

[toddmaci]

Donn,
Thanks for that information. I have a very small shop and would rather not have oil mist in it. I also think this one was used for HVAC. Not sure if residual freon hangs around. Do have an example of what a carbon vane pump looks like?

Thanks,

Todd

[rb99]

What size of area do you want to hold down?

Maybe the Feine vacuum would be enough.

RIB

[toddmaci]

Richard.
I am cutting a very small canoe orr with holes in the paddle end. It is 3/4 maple and I cut it in 3 passes very slow feed rate. I trida standard vacuum with gasket and it gave way

T

[coach]

Todd, are you cutting from a full sheet of 3/4 maple plywood?
If so do not cut completely through. Leave an "onion skin" then cut it with a u-knife.
If you are cutting from a small piece of 4/4 maple, say not much larger than the oar. I would try double sided tape. I cut lots of 3/4 hardwood plaques from a blank starting at 20" x 16". v carve first then I cut the profile. I use double tape and it works for me. I then run the part through the belt sander until the onion skin is sanded away.

[rb99]

I was thinking more about the dimensions than the thickness.

Is it 6" x 72" for example?

Once that is given there are many experienced vacuumites who can tell you the best way to go.

RIB

[toddmaci]

Richard,
The dimensions are roughly 3.5" X 36".

[ky_trikes]

If you want to go with a vacuum hold down, I agree that the carbon vane type oiless pump is the way to go. I bought a Gast pump almost 20 years ago from American Science and Surplus to use for a vacuum-forming machine. I finally got around to building the machine, but was disappointed with only 4" of mercury. I knew my vacuum box was not quite air tight, so I sealed all the leaks and got a better gasket, but the other thing, and the reason I wanted to post this, is that I discovered one of the four vanes was sticking in the retracted position. Once I freed the stuck vane and cleaned the pump (by spraying carb cleaner into the intake while it was running), I was able to draw 24" of mercury. Very pleased with this pump. If you do go this route, I suggest that before you buy a used pump, make sure you can find a wiring diagram for it, including the values of the start and run capacitors. I've also seen these pumps on Craigs list too.

[mikek]

Todd, Joe Woodworker has a kit available that has all of the parts required to put together a nice system. With HDPE fixtures and using maple, you should not experience much leaking. With dedicated fixtures you can cut through material and not worry about leaks.

http://www.joewoodworker.com/veneering/EVS/concept.htm

They have at least three choices of pumps to go with it. Both Gast and Thomas are good choices. The Thomas based system is $267.90 and the more powerful Gast is $448.90. Either will pull 24" of Mercury with no leaks.

[dana_swift]

I bought a Becker vacuum pump that delivers 28"Hg and lots of CFM at lower levels of vacuum Hg. You pay extra for that, but its so wonderful to have! The Becker pumps are equivalent with the Gast versions, either company builds great pumps. Oil-less carbon vane pumps are indeed very nice if you can afford one.

I started using low-CFM higher vacuum A/C models, but the Becker or Gast designs are intended for 24/7 operation. Once a month the machine requires lube, with an expectation of 12 months continuous running before vane replacement. I dont run it anywhere near that hard, so it will be years before that will be needed.

I am getting extremely good holding under very wide conditions on a BT-32. My system uses a 100# propane take as a vacuum "accumulator", and a programmable pressure/vacuum switch from Digikey that keeps the vacuum between 18"Hg and 26"Hg by turning the pump on and off.

Go the cheap route at first, then upgrade when conditions warrant. Keep your eye on ebay also, big pumps come up periodically at good prices.

I have posted elsewhere on the forum with photos of my hold-down table for the BT-32. Its running great!

D

[tkovacs]

Todd,
I have been reasonably successful at cutting small maple pieces (4"x6", 6"x6") using a recess cut into the spoil board that matches the maple blank. You can get extra pull by sealing all but the recessed area.

Terry

[ron_benevento]

HOLD DOWN TABLE.pdf (http://www.talkshopbot.com/forum/messages/312/HOLD_DOWN_TABLE-51913.pdf) (5.3 k)
I am going to use a handheld router to cut stock into various patterns each off which is to receive a full roundover. The attachment shows my intended plan. Q. Will a shop vac work for this hold down design or will it burn up.