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PCD bandsaw for cutting rocks

amaarahsan

Plastic
Joined
Sep 20, 2017
I am working on a 75cm (30") bandsaw that has a 1.5mm thick blade with 3mm diamond inserts attached to it. Due to the blade dimensions the gullet is set to move about 5cm in front of the wheels and the wheels do not have any tires. The blade is 100mm (about 4") wide and we cut granite, sandstone and marble with it.

The problem that I am getting is that due to the high cutting forces involved the blade either gets twisted laterally and out of the back roller and two the cut is not always straight and the blade drifts away from a straight line. We tension the blade hydraulically.

During the setup we place the roller guides such that both the side guides and the thrust bearing are in contact with the blade and we do not keep a narrow distance between them.

What I want to know from you guys is
1. Will it cause any improvement if we maintain a slight distance between the blade and the guides during the setup and why?
2. Installing crowned rubber tires, would they be helpful and why?
3. Is it somehow possible to change the direction of the blade if it does drift. Keeping in mind that with our setup we cannot turn the workpiece, in this case very large and heavy rocks ?

Thanks a lot in advance for some advice.
 
I do not know much about bandsawing. I do not know if you have a constant feed rate, or a regulated feed pressure. If pressure, there needs to be a proportion between feed pressure and band tension to keep the band straight in the cut. Maybe you are feeding too hard. If your feed is set to a constant rate, then if the band cuts too slowly, pressure will build up until the band won't stay straight.

I suppose you are cutting wet....is the water equally distributed on both sides of the blade, so the cutting segments are staying equally clean and free-cutting on both sides? Can the blade become unevenly worn because of hard spots in the stone?
 
The blade runs directly against the metal wheels. Could that be damaging the diamond inserts on that side? In a normal bandsaw damage to the teeth on one side will cause the blade lead to one side. Tires on the wheels would eliminate that.

Also check the alignment of the guides. Are they holding the blade parallel to the intended cut?

I run my guides with a very small clearance on the side of the blade, maybe .001", just enough to keep from binding. I think you will want to do the same. Roller guides can be set tight to the wheel.
 
The tension on a blade of that cross section would have to be vast, google bandsaw blade tension and it may help you find some answers.

Personally a large - super sized bandsaw is not the way would go for rock cutting, if you look up rock sawing on you tube you will find very very few examples of doing it that way and i think for very good reason. uneven segment wear will soon result in inaccurate cutting, anyone thats done wood or metal cutting with a bandsaw knows the slightest damage to the blades set or teeth will very much make it wander, cutting natural rock, even with diamond based abrasives your going to get a uneven wear and hence a natural drift in the blade as it cuts.

You don't mention it, but flushing is going to be key to keeping a straight cut, your also going to want great flushing post cut and at the various blade guides.

Feed force is another variable, too much will cause any band-saw cut to be inaccurate, there’s no free ride on this one, you may simply have to reduce your feed pressure.
 
On most bandsaws there is a provision to tilt one of the wheels With that you guide the bandsaw on the wheel
Do your wheels have a rim for the saw to ride against
The wheel has to be adjusted that it only just rides against that rim


Peter
 
I have only seen PCD bands up to about 1-1/4" wide for stone fabbing shops and hobbyists, no direct experience.

However, since you mention a 4" width band and no tires, it reminds me of a band resaw or even small headrig saw for wood. Such bands run without tires, on crowned steel wheels, and the bands are "tensioned" such that the band laid edge down on the teeth, describes a shape that is a segment from the bottom half of a traditional wooden barrel. The rule is that nothing on the band is tighter than the teeth edge. The tension across the width of the band matches a tension gage of the correct radius edge for the crown on the steel wheels. For 4" wide bands of 18 or 19 ga, the tension on a band to match a crowned pulley is about 30 to 34 ft radius of arc. To run the same saw on a flat pulley, it is tensioned to about 38 to 40 ft radius of arc.

"Tension" on a band refers to the curvature across the width when compared with a gage of a given radius edge that matches. "Crown" on a pulley means about what it sounds like. "Crown" on a band refers to how straight the back edge of a band is compared to a straight edge or concave back gage.

I will venture that whatever method the stone saws are kept on the wheels, any saw will wander if the tooth side is "loose" (longer) compared to the back side. I will guess that crown on the steel wheels & proper, uniform, accurately hammered or rolled (tensioned) bands will stiffen the band overall and make it run "straight" though the saw frame may need to be aligned with each new band, or as the band teeth wear.

Some of this is speed dependent. I do not know what speed stone saw bands run.

The only technological book on the subject that I am aware of it _Wide Bandsaws_ - _The Art of Saw Coctoring_ by Arthur Simmonds; published by Stobard and Son Ltd., London. ISBN 0 85442 016 9 My copy is 2nd Ed, 1980.

As may be imagined, quite a bit of the material relates to tooth shape and sharpening wide bandsaws for wood. But the material on hammering, tensioning, and weld repair of bands may be interesting. Also the theory involved in keeping a saw band on the wheels and sawing straight.

smt
 
What stress level are you tensioning to ?

Walking around in the guides, and bending when hitting the back roller leads me to believe your not tensioned up enough,
and your feeding too hard.
 
Hmmmm

I rip on BS with fences but any free hand work is a PITA to keep a cut from drifting as the cut kerf is slightly wider than blade so the cut is truly "free hand"- nothing keeps the cut straight except force of will and any drift of work piece will cause a rough cut.
I use a simple dodge to follow lines on stock:
I feather the work on the back of blade slightly and with this hard point to stop drift I can easily "steer" the work piece to spit a fine pen line "freehand".

As your work piece is too heavy to steer I would suggest a ball bearing feed table for work piece- I would think 1000lb slabs could still be worked through saw in this manner keeping the cut true..

Like these:

ball_transfer_table.jpg

For your work perhaps a pin set directly in back of blade in cut kerf would serve the same function and make finer work possible for your workers.
A photo of your setup and stock might make the whole ideal unworkable...
 








 
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