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View Full Version : Air cylinder to bandsaw damper?



Doc Nickel
10-21-2009, 03:33 AM
My old Wellsaw horizontal bandsaw has a sort-of hydraulic damper that really doesn't do the job. I recently picked up a handful of largish Bimba air cylinders, about 1.5" bore and around 8" stroke, 1/8" pipe (I think, I need to check) inlets.

So, a couple of questions: First, what sort of oil? Should I be concerned with compatibility to the ram packing, or would any hydraulic jack oil work? Motorcycle fork oil? ATF?

Second, I know this was discussed either here or on PM, but I'm having trouble digging up the thread. I recall there was some issue with filling the cylinder completely, due to the difference in volumes because of the ram shaft- Do we get around that by intentionally leaving an air bubble, or do you add an "accumulator" type of arrangement? How do the commercial ones avoid this?

The brand-new Wellsaw at the college has what looks a lot like my cylinder, with just a tube from the upper to the lower inlet, with a needle valve in between.

And third, any suggestions for a good needle valve? I recall there was some discussion about long and short needles and the like, but in this case, I doubt I'll need hairsbreadth tunability. :D

Doc.

dr pepper
10-21-2009, 04:04 AM
We have pedastal saws here that use a circular disc for cutting metal, and they are hydraulically damped, they use hygliss 32 oil, which is basically hydraulic oil, motorbike fork oil would do the trick so long as it doesnt attack the pneumatic seals, which it probably wont.
You need a seperate resorvoir as both sides of the regulator cylinder do not have the same volume, most cyliders are 2 to 1, so the rod (annulus end) end will hold less than the non rod end (full bore).
Also to work properly the resorvoir needs to be pressurised slightly so that theres enough pressure to make the spring loaded non return valve open on the return stroke, old ones so this with air pressure (you need special water based oil for these dont do it) and later ones use a resorvoir with a spring loaded piston, you could implement this by getting an old cylinder similar to the one your using for the regulator or maybe a little smaller, take it apart and put a spring on the annulus side of the piston, then use the full bore side as the oil tank, the spring will maintain slight oil pressure, youll need a 't' piece with a fitting on so you can fill it with oil (a grease gun works for this).
Accross one side to the other on the regulator cylinder you need the needle valve you mentioned, its just a flow regulator, you can buy off the shelf hydraulic ones, you can even use a gate valve, I've tried making a needle valve for a home build oil burner using a motorbike carburettor needle with some success.

Dawai
10-21-2009, 06:39 AM
With my robotic toys over the years, I found vegetable oil to be the most compatible with air cylinder seals.

I had a positioner using air over oil, before it would bounce and crash, after the oil through a orifice it would be rock steady. A needle orifice, with one way release.. that way you can lift the saw and not have to readjust each time. I have half a dozen on a shelf here somewhere.. if I could find one I'd send it.
You of course need a reserve to store the oil in.. is that the plan to use a second cylinder and a t-tap?
EDIT: add photo.
http://images.grainger.com/B293_64/images/products/1A861.JPG
Price is plumb ugly.. $40-$50.. and no valving descriptive. I'll look around the shop later today for you. Anyways, you can build a whole bunch of stuff, this works as you have saw them on other saws.. a one way that bypasses the orifice and the orifice works on the "other" direction down only. With a double ended cylinder, you don't even have to store the oil.. just let it fill the other end.. add a t and plug to fill oil into it.

Rustybolt
10-21-2009, 07:03 AM
Why not rebuild the original cylinder?

Michael Edwards
10-21-2009, 07:22 AM
So, a couple of questions: First, what sort of oil? Should I be concerned with compatibility to the ram packing, or would any hydraulic jack oil work? Motorcycle fork oil? ATF?
Doc.


I would use air tool oil, then you know it will be compatible.

ME

Dawai
10-21-2009, 07:44 AM
http://www.grainger.com/Grainger/items/4A789

I think this is it.. one way poppet valve, needle restriction in one direction only.


Air Line Flow Controls


Brass
2-stage needle.
Set screw secures selected needle position. Features include a brass body with stainless steel needle, internal stainless steel poppet-style check valve, and a knurled adjustment knob. Rated for 2000 psi max. (nonshock).
Sidebar note: well.. they don't like to be installed in a propane "metal smelter" furnace as a flow control. You get a nice flame around the adjustor where the propane has eroded the seal.. It wasn't a real big fire, don't you know... but it was exciting for a moment or two.

Circlip
10-21-2009, 08:06 AM
Think Dawai and I MAY be on the same wicket but you do state using an AIR cylinder??? So why all the posts putting OIL into it??

Can you not just use it as nature intended and put an air release valve on the "Bottom" end of the cylinder with a ball valve to allow an "Inrush" to prime the cylinder and adjust the fall with the release??

Regards Ian.

Sorry Dawai, just re-read your post #3

EVguru
10-21-2009, 08:12 AM
The problem with just using air is that the cylinder will also act as a spring.

I ended up with a broken blade on my saw when cutting thin wall tubing. I had the balance spring wound all the way up and when it hit the weld it bounced out of the cut.

wierdscience
10-21-2009, 08:14 AM
On the Wells saws the piston volume is equal to the rod volume so they cancel out.They are also plumbed up remote(at least on the bigger saws) so the valve can be located near the switch.

I have been thinking of adding in a solinoid valve inline with the down control,one that's blocked until the power is flipped on.That should allow leaing the feed setting alone when production cutting.

Dawai
10-21-2009, 08:42 AM
production cutting

Bragger... Ha... ohh well.. I dragged the last "made in America" (chinese) saw out to the road where it sit outside my gate for a "guy" to pick it up for about a week. Finally I gave it away again, the second time it took..

I now have a old Portaband saw I bought in the 80s.. still cutting.. sometimes a small shop that is enough.

FOR a big job, which I seldome get? I can hire the people at the steel store to cut to length all pieces for me. I buy in 20 foot lengths, but.. A job like a car trailer or other kind of big job with a cut-list.. I pay for the "real good saw" and smile as I grind and weld it up.

winchman
10-21-2009, 11:27 AM
"On the Wells saws the piston volume is equal to the rod volume so they cancel out."

I don't understand how that's possible, unless the cylinder has a rod coming out both ends. If it's only coming out one end, the effective area of the return side must be less than that of the piston.

The damper on the Dake-Johnson at the school doesn't have a pressurized system, and after several days, the cylinder has sucked in enough air that the saw won't stay all the way up. It still controls the descent rate well enough, though. We have to bleed the cylinder about once every two months.

Roger

Hal
10-21-2009, 11:45 AM
I think it was on this forum that someone posted a pic of a screen door closer that he adapted to his saw.

Hal

wierdscience
10-21-2009, 11:52 AM
"On the Wells saws the piston volume is equal to the rod volume so they cancel out."

I don't understand how that's possible, unless the cylinder has a rod coming out both ends. If it's only coming out one end, the effective area of the return side must be less than that of the piston.

The damper on the Dake-Johnson at the school doesn't have a pressurized system, and after several days, the cylinder has sucked in enough air that the saw won't stay all the way up. It still controls the descent rate well enough, though. We have to bleed the cylinder about once every two months.

Roger

They don't cancel exactly,there is still a greater volume on the base end.But they also have a longer piston than normal.The cylinder tube is about 22" long,but the stroke is only around 12"

The only time this system takes in air is when the saw's head is picked up too far.Even then it doesn't effect the feed.That might be the problem with the one you have at school.

dfw5914
10-21-2009, 12:55 PM
First, what sort of oil?
Doc.

DOT 5 Silicone brake fluid.

torker
10-21-2009, 09:08 PM
Reckon you forgot about his Doc...
http://bbs.homeshopmachinist.net/showthread.php?t=27773&highlight=Wells+saw
This setup works flawless and the air powered "up" is awesome for when you get really busy doin a bunch of cuts.
Russ

Doozer
10-21-2009, 09:33 PM
DOT 5 is not a good thing to use for an air cylinder. It is expensive, real expensive. Silicone oil is not a good metal lubricant at all. It might be slippery, but not a good lubricant. It allows galling of parts, especially soft parts or parts of dissimilar materials. Brake parts get somewhat around this galling problem, because they either use rubber cups to isolate the fluid from the pistons or they use a chrome piston in a cast iron bore. Iron tends not to gall, especially not against hard chrome.
I might consider anti-freeze for use in an air cylinder.

--Doozer

dfw5914
10-21-2009, 09:44 PM
DOT 5 is not a good thing to use for an air cylinder. It is expensive, real expensive. Silicone oil is not a good metal lubricant at all. It might be slippery, but not a good lubricant. It allows galling of parts, especially soft parts or parts of dissimilar materials. Brake parts get somewhat around this galling problem, because they either use rubber cups to isolate the fluid from the pistons or they use a chrome piston in a cast iron bore. Iron tends not to gall, especially not against hard chrome.
I might consider anti-freeze for use in an air cylinder.

--Doozer

DOT 5 is not that expensive, especially when considering the small quantity required. Galling and lubrication qualities may be theoretically unsuitable, but in practice DOT 5 works well as a hydraulic fluid in cylinders designed for air. I've done it, in an application similar to the application proposed, it works quite well, for real.

Doozer
10-21-2009, 09:56 PM
My experience with silicone fluid comes from working 10 years for a shock absorber company. Various oils can be specified in a shock absorber, depending on the application. Silicone fluids are often used because they are pretty stable viscosity wise, over a wide range of temperatures. In the rebuild department and from the test lab I have seen shocks with many cycles on them, the same models with hydraulic oil and some with silicone fluid. The silicone shocks always had galled bores and piston heads. The ones with hydraulic oil, were usually pretty good. The company also built gas charged lift struts, and the standard working fluid was pink glycol, and a nitrogen charge of course. The glycol worked well, even with stainless bores and steel pistons.
DOT 5 may be OK for slow speed, low cycle hydraulic applications, but there are better and cheaper choices.
--Doozer

rode2rouen
10-21-2009, 10:30 PM
I used an air cylinder, filled with ATF, to replace the damaged cylinder on the old Emerson saw I bought earlier this year. Works a treat.


Rex

http://i721.photobucket.com/albums/ww216/bjorn_toulouse/emerson10.jpg

dfw5914
10-21-2009, 10:31 PM
Interesting information, thanks. Would the leak-sealing "coagulants" in typical antifreeze cause problems with the needle valve?

torker
10-21-2009, 11:26 PM
Geez...use cheap ol' hydraulic fluid...add kerosene if it's too thick....as per sir Johns advice.
I use it in my air over hydro setup with an air cylinder in my job shop. It gets used a lot.
Never had a problem.
Russ

dfw5914
10-21-2009, 11:37 PM
Just depends on what type seals are in the cylinder.

dr pepper
10-22-2009, 04:58 AM
We have a few machines here that have standard air cylinders operating with hydraulic oil in them, not a problem, a couple have air one side and oil t'other.

Another way around the cylinder volume issue is to use a double acting cylinder, these have a rod sticking out of both ends, and have the exact same volume in each end too, in theory you could fill both sides and fit your flow reg from one end to the other, never tried it but it might work.

Doc Nickel
10-22-2009, 05:00 AM
Reckon you forgot about his Doc...

-I didn't forget it, i just couldn't find it. Didn't use the right search term. :D

rode2rouen, that's pretty much what I'm after, though my cylinder is a size or two larger. I'm still wondering of the displacement discrepancy is an issue. I'm assuming not, as yours and the aforementioned factory unit don't have anything like an accumulator. Is your cylinder completely full or is there an air bubble?

Dawai- That's pretty much the adjuster I had in mind. Let me know if you've got a spare, maybe we can trade some parts.

Doc.

rode2rouen
10-23-2009, 04:10 PM
rode2rouen, that's pretty much what I'm after, though my cylinder is a size or two larger. I'm still wondering of the displacement discrepancy is an issue. I'm assuming not, as yours and the aforementioned factory unit don't have anything like an accumulator. Is your cylinder completely full or is there an air bubble?




Doc,

The cylinder that was on the saw when I bought it was made by Clippard.
They are still in business in Cincy, OH, making a zillion different sizes. I called them and asked about using ATF, the guy said, "Go for it."

I searched "Clippard cylinder" on Ebay and found a guy about 5 miles from me with about a dozen listed of various sizes. The one I got is 11.5" long (including the end caps, but not the threaded mount lugs) and 1.5" OD.

I filled it with ATF through the pipe plug on the 3way block. When I filled it I made sure the piston was fully back seated, the fill hole in the 3way block was the highest point, and poured the ATF until it would hold no more. To say I have no air bubble might be a stretch, but if there is one, it ain't very big!

Maybe it's just me, but there seems to be a bit of overthinkin' goin' on about this. We're not talking about a brake system, or a lunar orbiter.............it's a downfeed control on a manual saw. What's a teeny air bubble betwixt friends?!?

As I said, it works a treat.


Rex

Hawkeye
10-23-2009, 06:18 PM
https://www.surpluscenter.com/item.asp?UID=2009102318134901&item=9-4313-A&catname=hydraulic

$10.95