PDA

View Full Version : cutting tapered grooves



darryl
01-28-2013, 09:13 PM
Started to groove some pulleys today for micro-V belts, J type. Took me awhile to find the actual specs, but with that down on paper I got one mounted up on a stub arbor, the cutter ground to shape, and had at it. Looks like I did everything wrong- things moved on me as I'm cutting the grooves, and the first three are not evenly spaced. I was plunging straight in, which in this steel and my setup gave a lot of chatter. The cutter is ground to 40 degrees, per spec, and has the correct tip radius. I have proper relief angles and it's sharp, but it's too difficult with the steel I used for the pulley. I did a test in brass, and the setup worked great, spacing was good, etc.

I'm thinking that this is just like a thread, though it doesn't spiral along. I should probably be setting the compound to 19.5 degrees and cutting the grooves with only the tip and the leading edge, dialling in with the compound. Because the cutter is such a narrow angle, I'm also thinking of doing it in two passes to keep the pressures down. I don't have a Monarch, or even a South Bend lathe :) Just my 8x18. The depth of each groove is minimum .072, so it is a significant load to just plunge straight in with that narrow cutter. In the brass it was a piece of cake, but not in the steel I used. I'm thinking I might remake the pulley in aluminum.

Comments, ideas?

Scottike
01-28-2013, 10:01 PM
I think your on the right track by approaching the op like a threading op, rather than a cutoff operation (plunging straight in).
You also might try using a cutoff tool to remove most of the material and then do a cleanup to spec with your form tool.
Don't forget - tool dead on center, and lots of cutting oil.

Toolguy
01-28-2013, 10:21 PM
When I'm doing a pulley groove, I grind the cutter to be less than the width of the groove. I start in the middle and plunge as far as it will comfortably go, then start working it side to side and deeper. That way I'm only cutting on one side and/or the end. It goes pretty quick and smooth that way. I just go straight in and work the carriage side to side. You can use an indicator or DRO to go the same amount either side of center.

TriHonu
01-28-2013, 10:50 PM
Here you go...

Making V-Belt Pulleys.pdf (http://www.green-trust.org/junkyardprojects/FreeHomeWorkshopPlans/MakingV-BeltPulleys.pdf)

doctor demo
01-28-2013, 10:50 PM
When I'm doing a pulley groove, I grind the cutter to be less than the width of the groove. I start in the middle and plunge as far as it will comfortably go, then start working it side to side and deeper. That way I'm only cutting on one side and/or the end. It goes pretty quick and smooth that way. I just go straight in and work the carriage side to side. You can use an indicator or DRO to go the same amount either side of center.

+1

Steve

darryl
01-28-2013, 11:23 PM
I re-made the larger of these pulleys from aluminum. Then I set up as for threading, with the compound set at 20 degrees in this case, for a 40 degree included angle. I re-calculated my positions, since I had a few wrong to start with :( Don't ask me how that happened- ok, I'll tell- it was an error made late at night when I was tired)

I did each groove with only the left edge and the radiused tip cutting. I still had chatter once I was in about 40 thou, but it was minimal. All the grooves came out good. I radiused the tops by rocking a 3 cornered file in each groove, and that worked out well also. This part looks very nice.

Next are the two smaller pulleys in steel. I really don't want to use aluminum here because of the wear factor- these are smaller, rotate faster, and the belt doesn't wrap around them as fully as it does on the large pulley.

I will do as suggested- use a parting tool to remove as much of the meat as possible, while leaving just enough for the grooving tool to remove the tooling marks.

I know that much of my chatter is coming from the flex between the cutting edge and the surface of the cross slide. I can do this pre-grooving without the compound in place, but I will have to go back to it to run the grooving tool again. I think it's time to get a more rigid compound mounting going on. Maybe it's time to get a more solid lathe-

One other thing- I have no way of measuring the depth of the groove directly, since the tang on the caliper is too thick to touch bottom. Instead, I went by the width of the tips. These are spec'd to be .008 to .013, so I just went by that. How could it be wrong, if the angles are correct and the spacing between grooves is correct-

Yet another thing- I'm using another contraption I made to move the carriage along by dialable amounts. There's a lead screw and nut, with a dial marked out for thousandths. It would be difficult to give a back and forth motion as has been suggested. I know that to do so would be an advantage, so maybe there's another project in the works- a lever actuated back and forth motion. Hmm-

MrFluffy
01-29-2013, 05:44 AM
When I'm doing a pulley groove, I grind the cutter to be less than the width of the groove. I start in the middle and plunge as far as it will comfortably go, then start working it side to side and deeper. That way I'm only cutting on one side and/or the end. It goes pretty quick and smooth that way. I just go straight in and work the carriage side to side. You can use an indicator or DRO to go the same amount either side of center.
That works for me too, I get the chatter the o/p described until I started doing this during pulley turning.

.RC.
01-29-2013, 06:22 AM
I have only made A and B section pulleys on the lathe, but I always just hack away with it then finish by swiveling the compound to the right angle..

EVguru
01-29-2013, 07:46 AM
These are pretty small V grooves being cut, so they shouldn't be too much trouble.

http://www.vbelts4less.com/assets/images/JRIB.bmp

When the ratio of pulley sizes exceeds about 3:1 there is often no need for grooves on the larger pulley. You can just treat it as a flat belt drive.

Forrest Addy
01-29-2013, 09:25 AM
You don't say what size lathe, the set-up you are using (three jaw on stub arbor, 4 jaw etc, collet, supported with tilstock cenrer), tool material, work material, coolant, cutting speed.

I've cut many a micro-V pulley using a nut arbor and center going straight in (plunging) using a travel indicator for pitch spacing and later a DRO. My lathe is 17" swing and it poops out cutting "M" pitch (.375" pitch) out. "J" (0.093") and "L" (0.187") no sweat even on HT alloy steel but I had to go pretty slow when I got towards finish depth.

The success of going straight in with a form cut of pulley V grooves depends on machine brawn. I've scored 34" cast steel elevator drums for 7/8 wire on a 48" American without a shiver yet 1/8" wide O-ring grooves were about the limit for a 9" SB. Size does matter.

If you are using a three jaw on your work arbor it may be slipping slightly in the jaws. When you have what hat amounts to a heavy form cut on a three jaw the arbor deflects a little in the smooth (non-serrated) jaws permitting slow axial movement. The arbor should have a shoulder to restrain it from axial movement and a center to support the end of the arbor and to force the arbor shoulder agoinst the jaws.

Steel? It might also be a good place for Tap Magic.

darryl
01-29-2013, 05:51 PM
This is an 8x18 lathe. I'm using the three jaw which has a central hole of about .877 inch or so. What I've done is turned a stub with that diameter on one end, then smoothed up the next 3/4 inch or so for the jaws to clamp down on. With the stub inserted into the chuck, it becomes a very rigid mounting arrangement. The rest of the stub is then turned to the diameter I need to fit the pulley onto, which became .985 because of the diameter of the arbor the pulley will fit onto. I did a shrink fit to hold the part onto the stub, then heated it again to remove. The pulley nestled right up to the face of the jaws. It's about as rigid as you can get with the 3-jaw.

I started doing the smaller pulleys today, using the same method. The first thing I realized is that the grooves for a J rib are only a little wider than my thin cutoff blade, so I ground a short 20 degree angle on both sides of it. I can plunge it in about 40 thou or so before it makes the groove too wide. Still, it will help as it will leave less material for the actual groove cutter to remove, and thus it will stay sharp longer- perhaps for the entire job.

I get chatter pretty much right away when I plunge the cutoff tool. What I'm about to do is to make up a 'jack screw' to support the bottom of the cutoff tool directly onto the cross slide surface. I'm thinking that this will take up some of the flex, and it will give me some idea of how much the flex actually does interfere with the various cutting operations. Of course, once I need to feed with the compound, I won't be able to use the jack screw.

One of the issues I have with grooving, or cutoff, is that the tool is flat on top and thus has no rake angle. I may need to create a custom holder so I can play with this and hopefully get a better result. I know about cutting edge height issues, and having the cutoff tool angled backwards to some degree will give me a way to set (and alter) this to suit.

darryl
01-29-2013, 08:12 PM
Success! At wrecking a pulley that is :( I cannot get these grooves done in steel with my lathe and set-up. There's just too much chatter, and both the cutter and the workpiece are getting damaged. I was able to face and bore the pulleys no problem, but getting a good groove- ain't happnen. I used the cutoff tool to begin with, but it just rounded over. Both ends of the cutoff tool are rounded- this must be a pretty poor piece of steel. It's stamped HSS, but it grinds bright sparks so I know it's not of the same grade as the other HSS cutters.

It's likely that the steel I made the pulleys from has some surface hardness as well. At least that's what it seems like. Poor choice of materials on my part I guess.

So- now to once again re-shape the grooving tool and make these from something else. What a waste of time- but I guess you live and learn.

becksmachine
01-29-2013, 10:28 PM
Almost any kind of cast iron (nodular, ductile, Dura-bar etc.) would be much easier to work with in this application.

Which is one of the reasons why so many sheaves are made from it.

Dave

darryl
01-30-2013, 12:01 AM
Cast iron, yes. A couple of times I've tried to obtain some bar but it was going to cost at least double what a steel bar would cost. Didn't seem right to me, so I didn't bite. Now I'll have to look into that again. I know it would have been a lot easier to machine these pulleys from cast.

I'm about done with these now- the last blank is shrunk fit onto the arbor, ready for grooving. I used aluminum, and modified the internal bore so they would have to be shrunk fit onto the shaft. Originally I wanted a tight slip fit, but this will work. In use they won't get hot enough to come loose, and I can always heat them to remove and replace with cast iron ones if they wear too much.

I've looked at the entire lathe set-up for sources of chatter. The last thing I thought of was maybe the headstock is not held as securely to the ways as it could or should be. Through all the tribulations over the years, it doesn't appear to have moved, and I've just checked to see if it's turning a taper. It seems like its bang on, so I'm not going to mess with it. The bearings have no detectable play, the chuck fits very snugly, everything is as good as it can be for this model. I probably would have had no problems with a leaded steel, but I used what I had, which was 'lets see if I can make these from this ****nium', which I think was something called 'superior'. Nothing wrong with the steel, just my selection of it for this job.

My part has cooled off now, so I'm on to the last few grooves and the job will be done.