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View Full Version : Bandsaw damper, revised



Evan
08-30-2007, 07:58 PM
I gave some thought to the design of the hydraulic jack damper, if you can call it a design, and came up with a much better and just as simple solution. It's mechanically correct with proper linkage geometry.

The bolt in the support plate is spaced by the washers so the assembly clears the side of the bandsaw. The washer stack is chosen so the nut is able to just bottom on the bolt shank, leaving the bolt free to rotate in the plate. I used a 7/16" bolt to avoid any deflection problems.

A short piece of tubing is welded to the top of the jack ram adjuster.

http://vts.bc.ca/pics2/damper1.jpg


Damper in place. The 3/8" bolt is simply clinched to the upper frame with a nut on each side.
http://vts.bc.ca/pics2/damper2.jpg

http://vts.bc.ca/pics2/damper3.jpg

Click the link to see an animated GIF showing the motion. The motion timing is not to scale.

http://vts.bc.ca/pics2/damperani.gif

Next I will experiment with the needle valve. When I have a solution I will post it.

PHiers
08-30-2007, 09:14 PM
I like the MKII better....:)

7018
08-30-2007, 10:00 PM
Thats really a good idea Evan, Somewhere I have a old cylinder off a wells bandsaw I need to find it and see if-n I can use it on HF saw....

rotate
08-30-2007, 11:26 PM
Can you explain the purpose of this modification to your bandsaw? I don't understand the benefit. I've seen hydralic springs added to larger bandsaws, but I thought those were use to assist in lift up the unit because they are very heavy.

Do have the valve fully open when operating?

MGREEN
08-31-2007, 12:01 AM
Evan,
Would this modification to the valve screw work?
http://i34.photobucket.com/albums/d140/MIKEGREEN555/DSCF0723.jpg
Using some sort of extra fine thread in the new plunger screw
would allow much smaller adjustment to be made.
A disk could be attached to the outer end and marked
in some fashion like a clock to serve as a reference.
Mike Green

Evan
08-31-2007, 12:05 AM
Horizontal bandsaws require some method of controlling the cutting force applied to the blade. Too much and a number of bad things happen such as excess blade wear, chatter, stalling and even blade breakage. The small bandsaws control the force by using an adjustable counterbalance spring. Adjusting it changes the effective weight of the saw and therefor the cutting force. This works quite well but not in all circumstances. In particular, the spring has no direct control at all over feed rate. The saw can free fall if it isn't in contact with the work. Feed rate will vary depending on the cross sectional area to be cut.

What needs to be controlled is not just the cutting pressure but the maximum feed rate. That is what limits maximum tooth chip load. When cutting a piece of material that present very different sections such as thin wall square tubing there is no correct setting of a spring counterbalance. It will either be too light for the horizontal walls or too heavy for the vertical walls.

A hydraulic damper controls the maximum feed rate while allowing maximum feed pressure. If the feed pressure would result in too much chip load because of a change in cross section the damper prevents that by retarding the feed rate. Both the counterbalance spring and the hydraulic damper have a place and can work together with the spring controlling the maximum feed force and the damper controlling the maximum rate.

Evan
08-31-2007, 12:15 AM
This is what the stock needle looks like in my jack. I expect most are similar.
The truncated end results in a loss of control as soon as it clears the tapered seat.

http://vts.bc.ca/pics2/nvalve1.jpg

I added a piece of bronze from some 1/8" brazing rod and tapered it. This has improved the control somewhat but not as much as I expected. I need to actually examine the seat to see what size the orifice is, not easy to do.

http://vts.bc.ca/pics2/nvalve2.jpg

ega
01-21-2014, 06:21 AM
Evan

I was sorry to see that this interesting thread had petered out. I've had my trusty bandsaw for upwards of thirty years but have only recently started using the more costly bi-metallic blades. With a view to protecting these against the problems you mention in your reply to rotate I went out and bought a similar jack and am in the process of fitting this (thanks for the idea and the excellent photos!).

I can see from some preliminary working of the ram that the control of the rate of descent is likely to be a key point and wondered whether you solved the problem of adjusting the valve to your satisfaction. Incidentally, it seems that my jack has a ball on a seat rather than a needle valve.

ega

vpt
01-21-2014, 10:20 AM
A simple double acting hydraulic ram can be used. Just plumb a line to complete the loop with a needle valve in the plumbing to control flow. It is essentially what the stock ones are on the bigger machines.

http://img.photobucket.com/albums/v82/Highpwr/Temp/7X12.jpg

drmico60
01-21-2014, 10:32 AM
Or you can make your own cylinder, see:
http://mikesworkshop.weebly.com/bandsaw-hydraulic-cylinder.html
Mike

ega
01-21-2014, 01:01 PM
Andy and Mike

Thanks for your posts which I have read on breaking for tea, having just got to the probable proof of concept stage in the workshop. I agree that the ideal solution for many would be a suitably-sized cylinder as fitted to the larger saws; others seem to have gone for alternatives on cost/availability grounds or because they like making things for themselves. I will have another look at the larger machines in my local stockist and will also make another attempt to join the yahoo group so that I can fully appreciate Mike's solution.

In the meantime, although this is the "revised" thread there is a good deal of useful comment in Evan's first thread including suggestions as to the stroke and bore of a cylinder suitable for the 4x6 saw.

ega

Forrest Addy
01-21-2014, 04:25 PM
At $125 to #$200 for an eBay replacement cut off saw feed control cylinder I ccan undestand why one would seek a more ecnomical approach.

A bottle jack is OK but I would think the seal friction high compared to the forces your application imposes. Seems to me that stick/slip may pose a problem.

I suggest instead of a 2 ton hydraulic jack you use a cylinder like this

http://www.ebay.com/itm/BIMBA-6-STROKE-STAINLESS-AIR-CYLINDER-MRS-176-DXPZ-/360833307192?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item5403575238#ht_1616wt_867

where seal stick-tion is measured in ounces instead of tens of pounds.

Also you need a needle/check valve like this

http://www.ebay.com/itm/BIMBA-6-STROKE-STAINLESS-AIR-CYLINDER-MRS-176-DXPZ-/360833307192?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item5403575238#ht_1616wt_867

which is expensive in this 2000 PSI model but much less from a pneumatic line. Of you can incorporate a check valve in the piston (if you can get the cylinder apart and back together) and use a plain needle valve to throttle descent. This eliminates a separate surge tank equal to the swept volume of the cylinder because the surge oil can be on the rod side of the piston.

The Bimba cyl and valve will allow a tidy and compact arrangement and you can mount the valve anywhere you can run tubing.

This assumes you have a little money to throw at the project. If your object is to use materials on hand then the bottle jack is an excellent expedient if you can accept seal friction.

ega
01-22-2014, 07:08 AM
Forrest Addy:

Based on my experience so far I think your point about stiction will be valid in my case. One used to be able to buy a 1.5 tonne bottle jack which might have been better in this respect.

The BIMBA cylinder looks very nice but for this approach to be economic I would need to find one here in UK - ironic that the eBay vendor is in Rochester NY and I am in Rochester, Kent! If the jack doesn't work for me I'll certainly consider a cylinder-based solution.

JCHannum
01-22-2014, 10:37 AM
Since the pressures encountered in this application are way lower than hydraulic jacks or pneumatic cylinders are designed for, a simple cylinder could be easily fabricated from common copper water pipe, or even PVC. The piston needs nothing more than an O-ring for a seal or a leather cups, which can also be shop made.

The rest of the plumbing is simple enough to shop fabricate or adapt readily available components.

EddyCurr
01-22-2014, 12:07 PM
Would a repurposed bicycle pump serve as an inexpensive starting point ?

.

ega
01-24-2014, 06:56 AM
Jim H:

I agree - as evidenced by the shop-made cylinder referred to above by Mike.

EddyCurr:

As a life-long cyclist I find your suggestion intriguing - (I did look briefly at the cylinder from an old-style car foot pump). Cycle pumps, at least those intended to be carried, are traditionally very lightly-constructed and whilst I think you are right in principle, in practice it might be better to build from scratch.

I am conscious that this thread was started by Evan and wonder if he has found the jack solution satisfactory in the long-term.

ega

Ian B
01-24-2014, 07:33 AM
Andy,

The use of a double acting cylinder looks like a nice solution, but how does it work? The swept volume of the rod side is less (by the volume of the rod) than the other side. Unless the cylinder has a rod coming out the other end as well, if the seals seal and the system is oil filled, it should be locked in its present position.

Did you only partially fill it?

Ian

EddyCurr
01-24-2014, 12:58 PM
Cycle pumps, at least those intended to be carried, are traditionally very lightly-constructed ...I agree. However, I have a floor pump of the 'high' pressure single-cylinder persuasion
that seemed like it might be a candidate for such a project.

Unlike some floor pumps that suffer from excessive product design, mine is an import
that has a simple bolt-on cast tread plate - remove that and have a ready mounting
boss for attachment to the saw. The cylinder wall has some substance, a threaded
top and a durable piston/rod assy. (I've lost track of how long this has been in service.
The hose failed at some point and something about it made replacement a headscratcher
but was eventually resolved - now it is likely to outlast me.)

All this aside, Bimba-like cylinders can be found somewhat inexpensively in this community.
Have you exhausted that avenue ?

Edit: Not where you might find the best options, but Amazon UK has some examples (http://www.amazon.co.uk/s/ref=sr_pg_8?rh=n%3A79903031%2Cn%3A1938841031%2Cn%3 A1939128031%2Cn%3A1939152031%2Ck%3Abore+rod+pneuma tic+cylinder&page=8&sort=price&keywords=bore+rod+pneumatic+cylinder&ie=UTF8&qid=1390585914)

Here is a 16x250 Double Acting (http://www.amazon.co.uk/MAL16x250-200mm-Stroke-Sinlge-Cylinder/dp/B00AO75UCM/ref=sr_1_188?s=diy&ie=UTF8&qid=1390585939&sr=1-188&keywords=bore+rod+pneumatic+cylinder) for 9 ish.

.

jlevie
01-24-2014, 02:09 PM
It doesn't take much of a cylinder to control a 4x6 band saw. I'd say that a .75" or 1" bore would be plenty. The cylinder needs only to be single acting. The ideal system is composed of a small reservoir, cylinder, check valve, needle valve for flow control, and a ball valve. The needle and ball valves are in line and the check valve is between the needle valve and the cylinder. Both circuits are obviously connected to the reservoir. The check valve allows the cylinder to easily suck in fluid when the saw is raised and the ball valve allows the saw to be locked at any position without changing the rate of sink.

It doesn't take much of a cylinder since the pressure is really low and thus it would not be difficult to make one. A simple o-ring will work, though a hydraulic cylinder seal would be better. Neither will last long if the bore of the cylinder isn't polished.

Years ago I had a 4x6 Clausing that had this as a upgrade to it's standard damper.

ega
01-25-2014, 01:02 PM
EddyCurr

Many thanks for the links. I had looked on eBay but not on amazon.

OT and BTW: when I bought my "Made in Western Germany" floor pump they were called "track pumps" for the same reason that track mitts were so called. It's very stoutly built and I have equipped it with an ingenious hose that helpfully permits the pressure in the hose to be released before the connector is removed from the valve. In UK we now follow the American usage and call them "floor pumps", a label which highlights the fact that the operator has only to push down whereas the portable variety requires the rider to push and at the same time resist his own effort in doing so.

vpt
01-25-2014, 01:13 PM
Andy,

The use of a double acting cylinder looks like a nice solution, but how does it work? The swept volume of the rod side is less (by the volume of the rod) than the other side. Unless the cylinder has a rod coming out the other end as well, if the seals seal and the system is oil filled, it should be locked in its present position.

Did you only partially fill it?

Ian


You know, this was talked about before on some thread on I believe the same topic. You may be right in the idea that the cylinder would lock. Possibly all that is needed is a single action ram and the fluid is plumbed from piston side to reservoir side? I always say and think dual acting because of the two fluid tapped points.

Also like others are mentioning pretty much any cylinder would work, just comes down to the plumbing. Personally if I were to build one I would go look at the local fleet farm in the tractor section and pick out the cheapest ram they have with the right stroke length.

JCHannum
01-25-2014, 02:39 PM
I was guilty of not checking all the responses prior to making my post. The shop built cylinder in drmico60's post is a variation on the cylinder used on Craftsman band saws. The flap valve on the piston and control valve incorporated into the piston shaft eliminate the need for fancy plumbing and difficulties that would be involved in adapting a hydraulic or pneumatic cylinder or the obvious complications in adapting a hydraulic jack.

Peter.
01-25-2014, 03:12 PM
Mine is partially filled with an air gap in the upper half. It's the same as the one in VPT's post #9. The cylinder extends far enough to allow the saw to go right up over-centre where no damping is required.