Been hopping around a dozen of scrap yard in town insearching of suitable supercharge; Instead found a sensible deal for a 4.5L patrol engine for nissan president for less then US200...
My mechanic friend is selling me the ideal to use that as vacuum pump... Very hard! He said just push the advance to max & mod the exhause valve to bleed the compression cycle... or just remove the exhause port & install a chech valve... something like that...
I'm really tempted & itch to explore the unknown but money is hard to come by... need to learn more before I get my head wet...
heres some numbers for 4.5L engine...
Made up a quick reverse engineering number on the fly & they look like this...
displacement : 4.5L per cycle
driven by a 4 pole 7.5kW (10hp) on 1:1 pully will suppose to yield an open flow of about 14000Lieter per minute or 494CFM lets just say if restriction come into play & I loose 30% & I'll still have about 10000l/min or about 345CFM (which is till a lot).
From the net, I learnt that when running compressor as vacuum pump, they don't have any problem to achieve 25"hg which is about 90% vacuum (27.9"hg for 1 atm pressure at sea level if I remember correctly)... so let just say I can only get 50% vacuum I'll still have about 14"hg... which is better then the 9"Hg magic number.
If I drive with 2:1 pulley, I'll surely have more suction power at half the displacement so half the flowrate & I still get 72.5CFM which is in the ball park of Becker vane pump's specs...
Other considerations as
Do I need to keep the radiator?
Stock lube oil system should not be affected?
Will keep the flywheel
will need a sizeable reservoir/accumulator to smooth out the pulse
Is normal car air conditioner pressure switch (which normally crack at 18"hg) suitable as the on/off vacuum regulator?

I'm all confused & any help is highly appriciated.

I too learn that a healthy patrol engine can ganerate 18~25"Hg of vacuum at the inlet during normal operation. Can anyone verify this number?

Ken, that engine's camshaft/valves are set up for 4-stroke, while a compressor/vacuum will be 2-stroke. I think it will make a very low efficiency vacuum pump that will waste a lot of electricity.

I'm not hoping for a highly efficient set up but something that is not tremandously poor... Beggers can't be chooser ;)
Yes, half of the cycle will be wasted, i.e. the squeeze & combustion stroke of the cycle will be rendered useless, come to think of it, the combustion stroke will cause serious inefficiency... I recon that alone will easily rob half the efficiency which is unacceptable even as a begger...
...I'm looking into the possibility to play with the cam shaft... it is possible to either grind a cam to get over that or have the 2 cams of the same profile... or maybe there is a cheapo alternative to bleed the combustion stroke.
BTW, the 4.5L engine is a V8 quad cam, i.e. double cam on each sides.

Might be easier to make new cylinder heads with simple spring-loaded valves, and disconnect the cams. (camshafts are not used in real compressors).

I'm leaning toward this method...tuen the engine to a 2-stroke compressor... am thinking of just a slab of steel with simple spring strip check valve like this
but I'm scapticle, it looks too simple to work well... sure ly the spring will fatique very quickly... or they won'd make a good tight seal...

Get the spring valves from real compressors?

WHY DIDN"T I THINK OF THAT!!!!
Gerald, You are a genius !

I may be late into this discussion but I think I remember that there were compressors constructed from a 2 cylinder engine that retained one cylinder as the power and converted the other to a compresser. Probably would work better with a diesel as a compressor. As a vacuum I think a diaphragm pump designed as a vacuum pump would be better. You probably need more volume than pressure, (vacuum) so you are looking at the more forgiving end of things.
roger

I 've seen a 16 cylinder diesel engine being converted to self propel compressor as describe by you, 8 cylinder for power & 8 cylinders as compressors... real cool...
I agree that in our application we need more volume than pressure... hence I'm not worry about the longevity of the engine, moreover, the engine block does has built-in water jacket if the event of over temperature. I've not encounter diaphragm pump with such high flow... if I can get my hand on one I will use it.
I'm sourcing for the suitable (affordable) concentric check valves for the pistons.

I found this:
http://www.woodweb.com/knowledge_bas...Effective.html

The expert in the discussion says the key is volume. I wonder if the best application would be to use the car engine to drive a big centrifugal fan that evacuates the air from a chamber. Somebody on here spoke of using something like that for dust collection. They blew air out of a small sealed room in their shop, connected the dust hoses to it and then once a month shoveled the chips out.

Roger,
Thank for the link, it is very informative.
The word "onion skinning" keep poping up, I did some google n the results turn out to be method to skin onion...
Could anyone explain that to me please.
Thanks in advance.

Ciao

more used for sheet work, when you router the parts you leave the last cut short by 1mm or so, just enough so that it stays part of the sheet.

once the cut file is done you slide the whole sheet off the cnc load new sheet start cutting, while cutting you punch your parts out of the sheet and if required clean up the edges of the cut with a small router with a flush cutter bit, this can be free hand or in a router table.

Thanks Gareth.
So that is onion-skinning, I've been doing that for a while. It happened unexpectedly. It started when I accidently has 0.1~0.2mm left on the cut.
Eventually I gave up. cleaning it is a lot of work & time consuming...
I recon for the vacuum table, this technique will only work on solid wood & other non-porous workpiece. Will it be effective with MDF?

I'm speaking from the viewpoint of total ignorance, but: My impression is that a vacuum system pulls vacuum through the entire spoilboard. When the sheet to be cut out covers the spoil board there is minimal flow of air needed to maintain vacuum. Once you cut through the top sheet, it would be like poking a big hole in your seal and your vacuum pump would have to pull enough volume to maintain negative pressure on the remainder of the sheet even with this leak.

Whats needed is a miracle glue that you can turn on off somehow!

something like gecko feet...

Or a vac mat. http://www.youtube.com/watch?v=xr3lf...eature=related

When I was laid up for a month with broken toes I looked into a lot of vacuum discussions. There is no cure for everyone's needs (at least I didn't find it) I did learn though if you plan to use a spoil board you will need a large vacuum with lots of displacement and cost go up. If you use vacuum pods you can get by with a lot less. I had a perfect video showing a vacuum pod system using a venturi and pods. He used Melamine as the table and positioned the pods all around where the cutter wouldnt go through. In the end of the video the waste had dropped down and the all keepers were elevated. I will try and find it again.

I have another puzzle, if we do wave carving on both side, can vacuum holdown work?

I think the vacuum seal would not work on the waves. Not enough contact area unless you left an undisturbed border and maybe used a foam backing to keep the waves from jumping around while you cut the second side. Maybe use the first side twice to make a mold then inject poly urethane foam to make the two sided wavy board.

Hmm... make matching seal with inject PU foam that is a brilliant idea!

lol, if all you want is a seal, you could use plaster of paris. I figured make a two sided wavy board mold so that you could mold two sided wavy boards!

Back to the vacuum: Would it work if you were pulling a vacuum through a 1/4" mdf board, then put a laminate sheet down for the vacuum to pull against, then use wax to attach the actual object sheet to the laminate sheet. Once the pieces are cut, a hair dryer lets you detach the cut parts. The engraving people use pitch or rosin as a heat activated adhesive, but with higher temps and higher adhesion. Actually I wonder why bother with the vacuum at all if wax on a reusable platen would work.

Hi Ken how thick you need it to be ,maybe you can do 2 and glue them together?

Lately I receive small but steady stream of waveboard carving on solid tropical hardwoos timber panels of about 20~25mm thick. Some times there are requests to carve the whole panel. when this happens, I'll have to run 2 g-code file with different clamping position. It I don't do something in the future, the vacuum holddown will be useless for such requests.
I am in progress of a vacuum pump conversion now, have not started the table, so I hope I can get as much info & incorporate as much useful features as possible.

[QUOTE=KenC;47854]Lately I receive small but steady stream of waveboard carving on solid tropical hardwoos timber panelsQUOTE]

any photo's sounds nice work

Ken posted a link to a picture in post 408 above. Nice work!

As per request.
Attachment 10879

good work Ken!

Poor Man's Vacuum Hold Down
 

Ditched the initial auto-mobile engine conversion as vacuum pump idea as Boyles' law told me it will be hot & I will have to have the radiator installed... That I don't like...

Saw what Buzz did here and the rest is history...

A few months of research, a few days work, and
A pair of vacuum cleaner motors & 5' of 2" PVC pipes, 2 Y-fittings, 2 elbows, 1.5m of flexible hose, 2 hose fitting, 2 PVC union coupling, a 49"x97" 1/2 in MDF board, 2 liters or lacquer, some thinner, 2 tubes of Epoxy glue & the fat lady sings.

A single zone 49"x97" plenum with a impossibly simple bleeder valve.

Bench Test figure
8"Hg vacuum continuous operation, capable of 10"Hg but the exhaust is near 100C within 5 minutes of running seriously too hot for my mental health, at 9"Hg it runs 80~90C still too hot for my comfort, so I operate it at 8~8.5"Hg where the eahaust is at 60-~70C at 38C ambient temp all day long.

Commissioning
Continuously operating for 10hours, 3 days at 38~40C ambient temperature. Motor temp consistently between 65~75C. Very noisy but no smoke :D
with just enough seal to get 8~8.5"Hg, cutting Merbao & Nyatoh of 2 sizes 1800mm x 600mm & 1900 x 650mm. max cutting depth 6mm @ 6000mm/minutes. Dia 50mm ball nose.

I apologise for the not so good quality pix from my cell phone camera but I hope some of you may enjoy it.
The Vacuum cleamer motor, with not so good packaging for shipping
Attachment 11741
Attachment 11742
Plenum
Attachment 11743
Plenum close up
Attachment 11744
All completed.
Attachment 11745

what is the blue pneumatic tube for - in the last pic

Be cautious of that noise
 

If you can put those noisy vacuum motors in a box without cooking them, that would be good. According to present theory, the sins you commit against your hearing now, may show up in 30 or 40 years as deafness: ehhh?? What???? CAN'T YOU SPEAK MORE CLEARLY???

Personally I think it is genetic, but the concerts, the trap shooting and driving at 95 mph with the windows down may not have helped.