Vacuum Hold down Recommend Size ? 10 hp / 20 hp or rotary vane

Vacuum Hold down Recommend Size ? 10 hp / 20 hp or rotary vane

We recently have been working with a company that orders small parts from us. They are are made from MDF and Plywood, We have a 10 hp Regen Vacuum Pump and it has trouble holding the small parts. Sizes range from 12" item to 8" items, they have started to order alot more each time and more frequently. We are looking into upgrading our vacuum system and the dealer has offered us 3 options. We currently use tabs to hold the items but it requires additional sanding to remove the tab and cost us alot of extra work.
Our work area is 4x8 but we only use 4x5 on this job type (Plywood is 5'x5')

1. Two 10 hp Regen Pumps ($1500 - Would only have to buy one)
2. One 20 Hp Regen Pump ($6000)
3. One 12 Hp Becker Vacuum Pump ($8000)

What option would you guys recommend - We are thinking about the 12hp Becker Pump the dealer say this will give us the best hold down but its the highest priced option. I just want to make sure well get a lot more pressure for the 80% price increase.

Thanks for Help
Robert

No first hand experience but I'd like the flexibility of multiple pumps allowing you to run as many as needed. FwIW, I read somewhere a but back of a commercial shop feeling like they finally had enough vacuum for small parts when they hit 40hp on a 4x8

I run a 48" by 48" Shopbot, with a 10 or 11 HP ( cant remember the actual Kw but its close to 11 HP) regen blower/vac. I use regular 3/4 MDF for a spoilboard, and have a plenum I made from 3/4" starboard (plastic).

That being said, I often cut parts as small as 1.5" to 2" by 10 or 12", or 3 or 4" square or round.

Vacuum hold down strength isnt the only "thing" - it will of course depend upon your cutting method. I usually use a 1/4" or 3/8" down cut spiral (down shear really helps hold down the parts VS upshear which can aid in lifting the part off the spoilboard). Feed speeds - the faster you want to run, the more vacuum you'll need. I run usually at between 240 and 480 inches per minute. Then the cut depth - for small parts I leave a thin onion skin, maybe 20 thousandths and go back and cut that after - very little sideways force on the part so less likely to move.

If it were me, I would run a second 10 HP regen, and have them running in parallel. When I am cutting, I usually just lay scrap melamine on the unused portions of my spoil-board, seems to work fine to stop unnecessary leakage.

It depends so much on each factor.. what bit/speeds/cut strategy are you using currently?

And what are the length or you parts, or square inch area?

Hey mark - thanks for the insight 40 hp would be way to much for our table. The company that makes our cnc offers a 40 hp pump but the rep said it would be over kill for our table size because we are only using 4'x5' . Two pumps I think will be the best route

Andrew - Yes there are many factors in play, we use a 1/4 compression bit on most of our plywood parts. This keeps the faces looking perfect. Our speed is 300 and we have a 11hp spindle - 16k-18k. We currently run two passes at .25" each and have two small .2"x.15" tabs on each item. What we finally decided is to go with the 12hp becker pump and have the 10 hp regen blower on backup if we need it in the future. I didnt want to buy another 10 hp and still not have enough hold down so we went for the "big guns" in my case :-) . Ill let you guys know how it works - Becker is also located 40 minutes from us so we can pickup the pump in a few days (didnt know this until sales guy told me )
Our 10 hp Regen Pulls 8 in.hg (inches of mercury). The Becker Pump pulls 27 In.hg.

If I were in the market for a bigger pump I would look at used. I saw a 14.5 becker for $5500. Tons of good used around. DAN

Hey Dan,

We tend to stay away from any and all used machines. We have bought two CNC and a blower off eBay in the past and they were garbage - paid a fair price but past owners had no idea what they were doing. Needless to say they got sent back within days. With production in mind we want something that plugs in and works and has a factory warranty. One guy said to quote "that vacuum doesn't have a lube plug " one picture later and a refund lol

Quote:

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Originally Posted by Robert Bonenfant

Hey mark - thanks for the insight 40 hp would be way to much for our table. The company that makes our cnc offers a 40 hp pump but the rep said it would be over kill for our table size because we are only using 4'x5' . Two pumps I think will be the best route

Andrew - Yes there are many factors in play, we use a 1/4 compression bit on most of our plywood parts. This keeps the faces looking perfect. Our speed is 300 and we have a 11hp spindle - 16k-18k. We currently run two passes at .25" each and have two small .2"x.15" tabs on each item. What we finally decided is to go with the 12hp becker pump and have the 10 hp regen blower on backup if we need it in the future. I didnt want to buy another 10 hp and still not have enough hold down so we went for the "big guns" in my case :-) . Ill let you guys know how it works - Becker is also located 40 minutes from us so we can pickup the pump in a few days (didnt know this until sales guy told me )
Our 10 hp Regen Pulls 8 in.hg (inches of mercury). The Becker Pump pulls 27 In.hg.

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I only have a 4 Hp spindle, but I regularly run 360 IPM, at 13,500 rpm to cut 12mm baltic birch plywood. Instead of two equal passes, I find a first cut at .45" climb cutting, and a second at .485" conventionally gives me a very good cut and being as the last pass is very low sideways thrust on the part, quite small pieces can be held down with even my regen blower which is more or less the same as yours. Key thing is that the sheets have to be clean and the spoil-board clean so there is a good mating.

With the Becker you should be laughing. I couldn't justify the expense, and I got a killer deal on a used Elmo-Rietschle blower. I would love to get a vane or claw type, high vac pump some day. Hope it works well for you!

Wanted to give a quick update - We received the new blower and started the setup. The footprint of the machine was alot larger than expected. Had to move my Cnc controller and table. My 10 hp regen weighs in at about 50 lbs and the new one comes in at 600 lbs. So far its holding down everything we have thrown at it - Successful equipment upgrade. I attached a quick picture of the two to compare, Discard all the wire and extra conduit - working on cleaning it up tomorrow :-)

Thanks for the Help Everyone Attachment 356573

Looks like a stud. Nice upgrade. How loud is it?

The title caught my eye, and I was curious...

I think the problem of 'clamping' a workpiece using vacuum is a fairly simple math problem if you know the lateral force applied by the cutter (or can guess at it) for a given feed rate. In simple terms the workpiece's maximum resistance to lateral movement is equal to it's weight X the coefficient of static friction.

To give you an example, I have to start making a number of assumptions; the first being the coefficient of friction. For wood-on-wood it is typically in the range of 0.25 to 0.50, so assume a (slippery) worst case of 0.25. Next is the weight of your workpiece - - so assume a 1 sq ft piece of 3/4" MDF at a weight of 1 pound. If you don't use any clamping at all, it would only take 1/4 lb of lateral force to start this workpiece in motion (F = 0.25 X 1 lb).

A vacuum clamp increases the effective weight of the workpiece. A spoil board with 0.25"dia holes at 1"OC under the same 1'sq workpiece has ~7"sq of holes (144 x area of 1 hole). So at 8"Hg, applied to this 7"sq 'hole', you get about 28 lb of 'clamp' (weight), and this gives you ~7lb of lateral resistance. If you increase the vacuum to 27"Hg, you get about 93 lb of clamp (weight), and this jumps you up to ~23lb of lateral resistance. ...And this is at wood's typically most 'slippery' coefficient.

As you can see, the real-world physical weight of the workpiece becomes irrelevant, as it is quickly dominated by more vacuum or increasing the number and/or size of your 'clamp' holes. Also, note that the result is independent of the surface area - except as it applies to the number of vacuum holes a workpiece is exposed to.

Anyway, hope this is of some interest or use - - and enjoy all that new suction!

Quote:

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Originally Posted by Robert Bonenfant

Wanted to give a quick update - We received the new blower and started the setup. The footprint of the machine was alot larger than expected. Had to move my Cnc controller and table. My 10 hp regen weighs in at about 50 lbs and the new one comes in at 600 lbs. So far its holding down everything we have thrown at it - Successful equipment upgrade. I attached a quick picture of the two to compare, Discard all the wire and extra conduit - working on cleaning it up tomorrow :-)

Thanks for the Help Everyone Attachment 356573

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Are you sure your regen was 10HP? at 50 pounds? My German one is between 10 and 11 Hp, weighs in around 400 pounds. Its quite large. Just fits under my Shopbot table. 3" inlet and exhaust.

Mark the model we bought is not loud at all, we can easy have a conversation 5 ft away at the machines controller, i was really surprised, i thought with all the extra power it would be extremely loud. From what the guy from becker said they have a sound damper built into this model.

Malcolm - Exactly Right, The only problem with running the math for us is most of the parts that we run are not square and have small areas and larger areas on the same part and cutout holes - Kinda like a anchor, Big at the bottom and skinny at the top so it makes it hard to judge the amount of vacuum and as soon as you make your first cut you start losing vacuum to the open cutting grooves. But your example is spot on

Andrew - Yes it was 10 hp from what the manufacturer plate said but it was a off brand. We had a republic 10hp regen blower on our last setup and it was double the size and alot better quality. I guess all pumps arnt created equal lol - Lagunas pump link below
https://lagunatools.com/accessories/...mps/10hp-pump/