Large band saw construction

[thespindoc]

I am trying to design a large band saw to cut at least 30 inch diameter pipe with 3/8 inch walls. Currently, I use a motor to rotate the pipe under a plasma torch but the cleanup is difficult due to the dross and the fact that as hard as I try there is always some wobble of the pipe with a wavy cut. A saw could make a cleaner and straighter cut but of course a saw large enough costs a lot of money.

Since I do not need to cut solid stock, I am thinking I could build up a machine from the design of a small saw like the Jet style horizontal band saw but just expand the throat and lengthen the blade.

I am thinking also of a column type design using a 1 inch blade with 10/14 teeth per inch. Maybe 2 large wheels or even 4 small guide wheels.

The powered hack saw is very intriguing like the ones made in the '70s by Kasto but I don't know how well they actually would work for pipe and there are some used ones out there but the design is certainly unusual. I am wondering if the scarcity of these is due to the fact that they did not work very well?

My question is how the various sized blades would behave with such a large piece of stock. Are such large saws unusual because there is not a need or because of the physical difficulties of such a long expanse of unsupported blade. Does anyone have any experience with cutting this sized material with a saw.

If I could get the basic mechanical questions worked out, it would sure be great to make it CNC with control of blade speed, cut speed, advancement of the stock, coolant and motor control etc. I know there was a post in 2006 from a man in the orient who was thinking along these lines but no further posts.

Thanks for any input or ideas.

Keith

[CarveOne]

Consider building a horizontal "V" cradle fixture with ball bearings where the pipe will lay in the "V". Rotate the pipe with a motor driven belt or chain drive at a low rpm. Mount an abrasive cut-off saw on a platform that is mounted above the "V" cradle to do the cutting. You would only need a low cost 10" or 12" cut-off saw for this, and make a deflector box for the spark shower if needed. You could also cut culvert pipe with a diamond masonry wheel. This should be a relatively low cost to build.

If you don't want the spark showers made by a cut-off saw, mount the upper half of a metal cutting bandsaw on the platform instead of the cut-off saw. The bandsaw throat will need to be wide enough to cut through the wall thickness but will not need to be the full 30" diameter.

CarveOne

[thespindoc]

Carveone,

Sounds like a possibility that the band saw could work. The biggest problem is rotating a 9 foot pipe smoothly and without it moving in and out. I currrently rotate 18 inch segments under the plasma cutter and there is always a little wobble and creep that I have not been able to completely eliminate. I might give it a try though. Others have suggested using a cold saw is the same manner but I like your band saw idea better. I still like the idea of a large band saw to make the cut without out rotating the pipe, if I just had one...

Thanks,
Keith

[Geof]

Originally Posted by thespindoc ...The biggest problem is rotating a 9 foot pipe smoothly and without it moving in and out....

It sounds like you do a lot of these. Perhaps it is worthwhile having some large split rings that clamp around the pipe and behave like a guide running between rollers. You should be able to get your wobble well below a blade width.

I also think re-considering the cold saw might be worthwhile. Bandsaw blades can wander and even using a smaller saw cutting on a rotating pipe there will be a lot of unsupported blade length. The blade is also entering the work at an angle which accentuates the wander; you might find you figure out how to stop the pipe wobbling but still cut a helical path with a band saw.

Actually I would be tempted to try building something based on a table saw. Rig up the cradle for rotating the pipe, slow the blade speed down to something suitable for a cold saw blade and rig some form of in-feed that brings the blade up into the work.

[CarveOne]

Plugs can be made to fit into the pipe ends and be held in place by bearing supports (kind of like placing a smaller pipe between bull nose lathe centers) to prevent end play movement. Building a sturdy enough fixture to support the weight of a 9' section of 30" pipe can be done but not cheaply. If the pipe ends are not very square this becomes problematic and the plugs can't rely on the ends for alignment.

Bandsaw blades will not usually make a square cut all the way through a 4" pipe, much less a 30" pipe. That was my reason for suggesting some way to cut just the surface only and rotate the pipe. Any rotating fixture must have a way to limit end play and allow for unsquare ends.

The abrasive cut-off disk will not be so likely to bend sideways unless it is under excessive pressure against the pipe. It tends to cut/grind more squarely and leave a better finish cut if not pushed too rapidly into the pipe. It should cut faster than a power bandsaw blade though. I would think that the consumables cost of the cut-off (chop) saw will be much less expensive than the plasma consumables. The blade size I would try first is a 12". Try a hand held angle grinder with a thin coarse abrasive disk and time how long it takes to just cut through the pipe wall.

CarveOne

[BillTodd]

Might be easier to keep the pipe still and move the saw.

Are your cut lengths short enough, to allow the saws rotational axis to be inside the pipe? i.e. Could you mount a circular cut-off saw on an arm so it could turn the saw though 360 degrees inside the pipe?

Alternatively, could you mount a saw on a hoop around the outside of the pipe?

[keebler303]

Isn't this common practice on oil pipelines and the like? I know there are rigs made for cutting pipe like this. I think you might be better off dialing in your process to get rid of your dross problem as I would think torch/plasma would be the most efficient way to do this. If you made a ring which clamped on the perimeter and the torch rode around the pipe, you should be able to get pretty nice cuts. You would have the ability to true up the ring before starting the cut, then you know it is straight ahead of time. Check some of the home built oxy torch cnc tables to see the quality of cut you should be able to get with the proper feed speed and torch setup.

Matt

[thespindoc]

I found a great company in Cincinnati called Weld Plus during some internet searching www.weldplus.com. They have many pipe cutters both used and new as well as pipe rollers of all sizes also new and used. There is quite a selection of anything one might need for fabrication - positioners, welding lathes, welding chucks etc. Tomorrow I will give them a call for some advice. Maybe tuning up the plasma cutting method with a better roller mechanism is the quickest and easiest. Hope also to test cutting my material with a band saw and cold saw tomorrow as well.

Thanks for all the great brainstorming!

Keith

[jpgdesigns]

Check these guys out... http://vernontool.com/ pipe cutters are their business.

[thespindoc]

Originally Posted by jpgdesigns Check these guys out... http://vernontool.com/ pipe cutters are their business.

That link really helped. They are doing what I was imagining with abrasive saws and plasma cutters by rolling the pipe underneath. Great videos of the machines in actions. Thanks again!

Keith

[langwadt]

found of something that might help in a very old book about welding.

-Lasse

[thespindoc]

I appreciate everyone's great suggestions! I have decided to seriously pursue the band saw method. The plasma cutter works and I know I could further improve on it but it has to be attended constantly, creates a black powder mess, leaves a grooved edge with dross that must be ground even under the best conditions, and costs quite a bit of money in terms of air compressor time, electricity and consumables.

This ring cutting is a very time consuming process that must be automated as much as possible for this to make money for me. The pipe cutting chain, wheeled walkers and ring bands require cumbersome repositioning adjustments when making 30 cuts on a 9 foot pipe. They are also very expensive to purchase from $1000 to $4000. No method with plasma or torch is satisfactory to me so I want to use a saw.

Anything such as a small band saw or cold saw or abrasive saw mounted on top of the pipe might work but require rotating the pipe and create dust, sparks and possible wander of the blade plus will go through many blades. My feeling is that a band saw with a 2 inch blade set up in a serious band saw configuration will do the quickest, cleanest and most true cut with the least long term cost.

I have a full machine shop with large CNC machines and automatic saw etc. plus the electronics abilities to make whatever I need. Here is an idea... 2 motors on top that move the frame up and down through a lead screw either slaved or 1 motor with sprocket and chain linkage. Counterbalance. 4 salvaged automobile wheels mounted on hubs with portion of axel on one mounted to drive motor with gear reduction. Still considering fabricating the wheels myself. 2 hubs with screw tightening mechanism. The entire frame is depicted from the side as being vertical but it will actually be tilted about 30 degrees backward.