[mrquacker]

I need to use a 140 tooth, 1.5" OD, .078" slitting saw to cut a whole bunch of thin wall (0.05-0.08") stainless and titanium. Ideal calculated rpm is 120 or so, and feed of 4.5ipm. So far I've tried a couple different combinations and the only one that did not stall the spindle was 350rpm, 4ipm. Checking actual rpm with a laser tachometer shows closer to 300 while in the cut. That cut also drops to 250 or so, then stalls the spindle when it reaches the last 1/2" of cut, and needs the ipm reduced even further.

Any suggestions? Any way to get more power out of the motor? The load meter barely moves.
Is there a way to add a 3rd pulley to the side and gear it down some more? That would let the motor work at higher rpms where it has more power.

[WOTDesigns]

A side cutting saw is much freeer cutting and requires less torque since the chips arent full slot width. Thwre is a thread on PM i think right now about grinding every other toothe on opposing sides to simulate a similar result. Have you looked at using one?

[tmarks11]

You could always just replace the low range pulleys so either the one on the motor is a smaller diameter or the one on the spindle is a larger diameter.

The only repercussions of that is that it would eliminate some of the overlap between low and high range.

You would also have to figure out how to edit PP config file to adjust the reduction ratio.

[mrquacker]

A side cutting saw is much freeer cutting and requires less torque since the chips arent full slot width. Thwre is a thread on PM i think right now about grinding every other toothe on opposing sides to simulate a similar result. Have you looked at using one?

Well, I already have the blades, so this is what I'm using. I'm not buying anything else right now.

tmarks11
You could always just replace the low range pulleys so either the one on the motor is a smaller diameter or the one on the spindle is a larger diameter.
The only repercussions of that is that it would eliminate some of the overlap between low and high range.
You would also have to figure out how to edit PP config file to adjust the reduction ratio.

Sure could, but I am not taking the machine apart for one job. Its long term, but I have other things to work on in between runs. What size pulleys does the 770 use? Where can I buy them? I don't have a lathe to make anything on.

Taking the PDB off though, and installing a bracket in those mounting holes with an idler pulley off to the side should let me add a second belt going from the motor, to the idler, then to the spindle, giving a 2:1 or better reduction.

[tmarks11]

Taking the PDB off though, and installing a bracket in those mounting holes with an idler pulley off to the side should let me add a second belt going from the motor, to the idler, then to the spindle, giving a 2:1 or better reduction.

Lot of work when you could achieve the same reduction just by replacing the pulley on the motor (easier then the one on the spindle, since the motor one would be available as a stock metric size, and it doesn't take much disassembly to swap it out).

Quite a few blades there, you must have stumbled on a really good deal!

[rowbare]

Can you do a circular interpolation around the tube you are cutting? I think that is your best chance of success with those saws.

bob

[mrquacker]

Lot of work when you could achieve the same reduction just by replacing the pulley on the motor (easier then the one on the spindle, since the motor one would be available as a stock metric size, and it doesn't take much disassembly to swap it out).

Quite a few blades there, you must have stumbled on a really good deal!

What kind of pulley does the 770 use, do you know? Where can I get other sizes?

Can you do a circular interpolation around the tube you are cutting? I think that is your best chance of success with those saws.

bob

I'm slitting them lengthwise. I can give it a shot, but I'm not sure how well trochoidal milling will work out.

[sin_arms]

Is it a really good job where you might be better buying a different machine?

[TurboStep]

...then stalls the spindle when it reaches the last 1/2" of cut...

How long is the cut? Reading between the lines it appears that the cut isn't blazing, but it's getting the job done until the last 1/2" - is that about right? From later comments I also gather this is tubing. How are you holding these tubes? Is it possible that the slot is closing slightly as the cut progresses and clamping around the cutter?
Step

[handlewanker]

Hi........lots less hassle to buy in a smaller diam cutter.....that way you can get more torque for less work than re-working the mill components.

If the cutters were bought for that job, can they be exchanged for a smaller diam?

You should also mount the tube on a mandrel clamped longways with a slot to clear the cutter that held the tube cut from closing when the cut is almost through.
Ian.

[tmarks11]

Hi........lots less hassle to buy in a smaller diam cutter.....

I think the OP already said that is not an option. I think you can see why:


And they are 1.5" OD. The smallest blades of this type are 1", which would change his calculated rpm to 240 rpm... which probably isn't going to significantly increase his torque.

Let me get the stupid question out of the way: did you have it mounted so the spindle rotation matched the arrow on the blade? They don't cut as well spinning backwards but they will still cut.

The ringinator website recommends 60-75 sfm for SS and titanium, which corresponds to 160-200 rpm.

What is the blade thickness?

[mrquacker]

Couple things to note, this is the smallest diameter cutter that is usable for what I am doing.
I plugged in all that tooltable data into Gwizard and am using those F&S

Yes, I made sure pointed and spun the right way.
Would I get any more torque out of the motor if I ran it in reverse? I can just flip the blade over to get it cut that way.

I built a fixture to clamp it all together. Two pieces of 1/4 aluminum with V grooves in the center to line up the tube, with a row of bolts on both sides. One of the pieces has a slit cut into it for the saw to go through.

[tmarks11]

Would I get any more torque out of the motor if I ran it in reverse?

nope.

Did you try slitting with maybe 3 passes of 0.020"-0.030"? Or are you cutting full depth (0.05-0.08") in one cut?

One of the problems here is this is a 140 tooth saw. So with your low feed rate it is taking really tiny chips and probably work hardening the SS as it goes. Your chip load at the 120 rpm and 4.5 ipm is 0.0003". It should be at least 0.001". More RPM just makes it worse (300rpm at 4.5 ipm is 0.0001... so you are grinding the part instead of cutting it).

Try running 200 rpm and 24 ipm, and reduce your DOC to 0.020" and see if you can get a pass without binding. If that works, try the next pass a bit deeper. NOTE: this is all theoretical to me, as I don't do much with fine jewelry slitting saws like this.

[handlewanker]

Couple things to note, this is the smallest diameter cutter that is usable for what I am doing.
I plugged in all that tooltable data into Gwizard and am using those F&S

Yes, I made sure pointed and spun the right way.
Would I get any more torque out of the motor if I ran it in reverse? I can just flip the blade over to get it cut that way.

I built a fixture to clamp it all together. Two pieces of 1/4 aluminum with V grooves in the center to line up the tube, with a row of bolts on both sides. One of the pieces has a slit cut into it for the saw to go through.

Hi, would I be right in saying that you are holding the part in a fixture like a pair of vice jaws that have vee grooves to locate the tube?

First of all the tube will close in if it's not supported on the inside, like on a solid mandrel with a slot running down the middle to clear the saw.

With a solid mandrel being a good fit in the bore for location, you clamp the tube across the ends faces......I can't imagine trying to hold a tube when it's cut through one side without it closing in on the saw blade.

I also could not imagine that a thin wall tube could grip a cutter with enough force to stall the spindle.....unless it's being clamped across the tube diameter.

What is the OD of the tube and it's length?
Ian.

[mrquacker]

The entire fixture sits flat on the mill table and is held down with clamps.

I'll also try the idea of taking it in two passes and see how that works out. I could also try programming some trochoidal toolpaths and see if that works.

[handlewanker]

Hi......judging by the amount of cutters you have "in stock" and this is a high volume job.

I think I would have a solid insert inside the tube with a slot milled down it's length to clear the cutter.....this would prevent the tube closing down when the cutter gets to the end.

I've used a similar method to cut stainless tubes down one side while the tube was held in a vice mounted vertically against an angle plate.......the vice jaws being profiled to hold the tube with the insert stopping it from closing down.
Ian.

[mrquacker]

I'll give it a try, but there is a bit of variation in the inner diameter from part to part. Also there are a bunch of different diameters to deal with, it's not just one size.

[handlewanker]

Hi....inside diam variation and different diams.........that will cause a problem.

If this is a no win and can't solve the problem situation, then anything can be explored.

Sometimes a problem is 90% set up and 10% actual work....BTDT.

One way I would explore if it were my problem and that is an expanding short bung that you place in the tube at each end and the middle......maybe only one at the far end.

An expanding bung is just a short round piece of solid material of the right diam, and a hole through the middle with a split to one side......if the hole has a thread at one end to take a tapered body screw, then tightening the screw will expand the body enough to grip the tube and cater for any variation around that diam.

The expanding device can be a tapered steel pin with a thread for a nut which is much simpler to make.

You would need 3 of these "devices", one at each end and one mid way to hold the tube open when it's slit, the mid way one needs a long screw driver or rod with a brazed on socket wrench to tighten the screw.

It would be impractical to think of a long expanding mandrel, although they do exist for holding tubes, bushes etc in lathe work, but rarely exceed 150mm in length.

You could use the screw from a masonry anchor bolt for the expanding device as it has a taper at one end which will cause the split bung to expand when tightened......an additional tapered washer at the nut end would be better.

You'll need to slacken the nuts off to remove the devices from the tube and give them a tap with a soft punch to break the grip of the taper.

BTW.....a hard rubber plug with a screw and nut can also be persuad4ed to expand in the tube.

I hope this makes some sense.
Ian.

[handlewanker]

Hi.....just had a thought........if you can get some machinable wax......maybe even candle grease..... it might be simpler to melt it down, fill the tube and melt it out afterwards........the wax, being fairly hard, will support the tube from closing in and is totally recoverable......it's also universal for the tube diam variation.

Lead can be a solution too but you'll need lots of heat etc.
Ian.