Anyone for a DIY Cold Saw?

[damae]

Cold saws sound like the ultimate metalworking saw, and everything I've read about them makes me want one! Unfortunately, a new cold saw is more expensive than most of us probably paid for our (used) full-sized Bridgeport mills!

Today I got a close look at one and realized that there doesn't seem to be much to such a saw. Just a special blade and a geared-down motor. This seems like a prime DIY project. Am I missing something? Is there something complicated about a cold-saw that makes it really expensive?

[WhiteTiger]

Slow speed drive motors are pricey, accurate gear reductions are pricey. With a cold saw, you can't cut corners on the articulations, they have to be rock solid and accurate or you will be eating expensive blades.

Basically, they cost out the yang because they are (and have to be) made to the standards of metal working machine tools, not to the much looser standards of woodworking tools.

Bit of "buyer beware" applies with cold saws, as I've seen some really flimsy dry cut saws offered for sale under the misleading name of "cold saw". In general, if what you're looking at has pressed or stamped steel table/vise/articulations then you're looking at a dry cut saw. Another way to tell them apart is the ratio of blade size to cut capacity; a real cold saw will use something like a 14" blade to get a 4" cut capacity and almost all of that dead 6" center will be taken up by the mounting flanges. A dry cut saw on the other hand will not have blade support much if any larger than a decent woodworking table saw.

Rigidity, rigidity, rigidity are the big three with cold saws.

Hmmm... seem to have run that 2 cents into a couple of nickels... time to shut up


Tiger

[damae]

..... Rigidity, rigidity, rigidity are the big three with cold saws....

This, among other things you said, shows me that I will have to build it heavy and solid, like any other machine tool. I see that a the smaller manual cold saws weigh 600 lbs and larger automatic ones can outweigh a Series I Bridgeport! Right now, I'm thinking of making a very simple 90-degree-only cold saw, since that is 99% of what I need it to do. No miter cuts. This should really simplify the design and allow me to make the one pivoting movement rigid. (feel free to correct me if this is wrong)

Gearing down sounds easy -- just a two or three-stage timing belt reduction. I have a lot of 1" L-series timing pulleys laying around that I can use for this. Of course, I say that not knowing what speed range I really need. Primarily, I'd like to cut aluminum. Steel occasionally. What speed is appropriate for a 300mm blade with 240 teeth?

Hmmm... seem to have run that 2 cents into a couple of nickels... time to shut up

Not at all! Everything you said makes sense. Before I make a go at this, I need a little dose of reality and some practical experience. Thanks for both!

[WhiteTiger]

Believe it or not, a 12" ~ 14" blade cold saw will be running the blade at somewhere around 100 rpm. If two speed, it may have a low of 70 or 80 rpm and a high of 120-140 or so.

You'd probably want to look around and find a reliable source for blades, choose a blade size/cut capacity, then look at commercial machines of that size to get your spindle speeds.

btw, on the spindle you'd want to figure on having your fixed mounting flange be an integral part of the spindle itself. For DIY you could probably get away with making it a beefy welded on part if you had the thing normalised after welding. The big consideration is you want the pressure face of that flange to be machined during the same setup as your bearing seats to ensure parallel planes.

Picking your blade size and style beforehand will help with mounting too, as some sorts use keys or positive drive pins/through bolts. I think MSC lists some cold saw blades, and the catalog illustrations would probably help.

I do agree that the prices of the machines are bafflingly high, and it has always seemed to me something that would be a great DIY project. (just never had enough need to justify doing it)


Tiger

[WhiteTiger]

Got to questioning my recall after that post and did a fast google. Here's a link to a page for benchtop cold saws. Notice the rpms... I was a bit high (I plead oldheimers)


Tiger

[damae]

Thanks again, Tiger!

Very good advice about machining the spindle! Sounds like that is the key.

I do agree that the prices of the machines are bafflingly high, and it has always seemed to me something that would be a great DIY project. (just never had enough need to justify doing it)

And speaking of justification, check out this line of logic: I don't currently have a lathe, but I need one to help build my cold saw. I need the cold saw to help chop up my steady source of aluminum scrap (6-8' long extrusions) so they will fit in a crucible for melting down. The crucible furnace will help me cast parts to finish my mill. The mill, in turn, will be extensively used to make the cold saw. Haha!

People ask what I'll make with my CNC mills, and I think I'll stop telling them about all my ideas I want to build. Instead I'll just tell them I like using my tools to make other tools!

[damae]

Ok, so I will use two identical reducions of 3.4:1. That's a 1140RPM motor driving two identical reduction stages: 24tooth to 82 tooth pulleys. I already have the 24t pulleys and will use my the Bridgeport to make the giant 82t pulleys!

This is going to be a long-term project. I'll start in earnest after I get my mill finished.

[CNC Pro]

This is an interesting project! I too have wanted one of these saws, but price is always the issue (even auction units are pricey!).
I was looking at the link posted by WhiteTiger, and recall seeing a hydraulic reduction/drive unit that looked very similar to the reduction of the saw in the link. Could a hydraulic drive be an easier drive system to control at low RPMs (and offer variable speed)? Living in a farming community, I see many applications using these type of drives, they offer VERY heavy-duty construction (i.e. large diameter keyed shafts and castings).

[gus]

TO cut aluminum, you want a high speed cold saw, 3500 rpm or so. A power miter box works just fine, especially since you are only going to melt it afterwards

An yes, my Fully auto non ferrous cold saw weighs over 1500 lbs

[dkowalcz]

Been thinking about this myself as well, the bandsaw I use now requires two milling passes to true up the stock squarely. With a cold saw, I could eliminate the milling ops, with an auto cold saw, I could save a lot of work indeed!

All it is is a one-axis mill so in principle there's nothing to it, but the forces are large owing to the cutter size so things need to be pretty beefy. As it stands, I haven't figured out how to build the gearbox for under $500, and I'd have to farm out the spindle machining, but it's on my list of projects as well. And as Whitetiger points out, even a small capacity cold saw (I'm thinking 2" sq max) needs a big blade since it's round.

Planning to weld a bunch of heavy steel plate and such for the framing and arm and such, it'd be fun to use up a lot of the junk lying around.

[WhiteTiger]

Plenty of places to buy worm gears and worms. MSC has a fair selection starting with a 6 pitch set for around $200 with 20/1 ratio.

Or you could consider cannibalising the worm gear box off your band saw. If it's like mine it's one of the little cheapies and probably cost you around that same $200 figure.

One convenient thing about a DIY cold saw is the nice low speeds; you can use inexpensive taper roller bearings rather than paying out the yang for high end ball bearings.


Tiger

[dkowalcz]

Yeah, I'm using the $200 cheap HF bandsaw all right, how'd you guess? I should join the support group for it one of these days.

So I pried the cover off the gearbox to take a peek when I first got it, and although I haven't done a calculation to make sure, I'm pretty sure those gears won't pass muster for cold saw duty.

I'm figuring 2hp continuous is about the bare min. I can get a full gearbox for $500 or so, just the gears for $200 is good but I need to add bearings and shafts and time, all pesky detail work that could go into building the saw. Naturally I'll want to make it full auto if possible - mostly I need to convert 12' lengths to as many 2" lengths as I can get!

Noticed most of the saws are hydraulic - any reason not to use a ballscrew with a triangle configuration for the swingarm? I'm thinking the GB and motor can go opposite the side of the pivot where the blade is - transfer the force with a heavy chain. This way the weight of the motor and GB biases the blade to be out of the work, and the ballscrew forces it in. Naturally a chip cover for the screw is in order.

That would make it easier to integrate the controls for the bar advance and vise, programming the lengths, and so on if it's all driven by computer...