Bandsaw damper, revised

[Evan]

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.




Damper in place. The 3/8" bolt is simply clinched to the upper frame with a nut on each side.




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]

I like the MKII better....

[7018]

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]

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]

Evan,
Would this modification to the valve screw work?

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]

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]

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.



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.