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Re: Milling a helix

Posted: Sun Jun 24, 2018 3:22 pm
by Harold_V
GlennW wrote: ↑
Sun Jun 24, 2018 5:56 am
Harold_V wrote: ↑
Sun Jun 24, 2018 4:42 am
...as the carbide end mill performed well beyond my expectation.
I'm curious as to why you had concerns about the carbide end mill. I find them to be much sharper and provide a much better finish than HSS end mills.
No concern about the end mill, just the quality of finish I'd achieve. Being a moving surface, I knew that it had to be akin to one that was polished, if I hoped to prolong the life of the gear, which is bronze. While I knew the finish would be good, I didn't expect it to be as good as it turned out. That was a pleasant, and very welcome surprise.

The end mill, being only 3/16" diameter, was run as fast as the spindle would go (4,200 rpm). The resulting chips came off without discoloration. My logic was to reserve the carbide for only the finish cuts, so it would remain sharp. Seems to have worked as planned.

H

Re: Milling a helix

Posted: Sun Jun 24, 2018 3:44 pm
by Harold_V
Dave_C wrote: ↑
Sun Jun 24, 2018 1:37 pm
I find them to be much sharper and provide a much better finish than HSS end mills.
I'll have to agree with Glenn, I've gone to all carbide end mills which are all made for specific purposes. 3 flute with special coatings for aluminum and 4 flute and a different coating for steels.
When I closed the doors on my commercial shop, I really hated the machines. I was burned out beyond belief, and didn't care if I ever saw the machines again. That was back when coated cutters were in their infancy, so I didn't grow with them. While carbide end mills were available, they were exceedingly expensive, so they were used only when absolutely necessary. I owned precious few.

Fast forward to today, where CNC cutter grinders are the norm, and carbide has been drastically improved. The cost of carbide end mills is often cheaper than HSS equivalents, so I've added several when the deal came along. I can remember when the market crashed and one of the makers was offering them in quantity at very attractive prices. I paid something like $4 each for 10, single end, ΒΌ" diameter four flute. I like them, but I'm well stocked with HSS end mills, so the carbide end mills are still reserved for those occasions where they are required. Don't know if I'll ever get over my old habits! :D
I had some .200" slots to cut .500" deep in aluminum. Made with .125" carbide end mill, 2700 RPM, a little WD and shes good to go.
The extra benefit if carbide is the added stiffness, which makes cutting straight slots a lot easier. Given your situation, I'd likely do the same thing, especially if my old stock of HSS end mills didn't include a new, sharp one. The only difference is I'd run it faster, but only because I can. I can remember when my fastest spindle speed was 2,700 (my first Bridgeport). Can't use too much speed when running those small end mills. My setup with the worm tolerated 4,200 for the finish cut, and it likely would have taken more.
Not intended to get the thread side tracked so congrats Harold on the setup and the finished product. That's some pretty out of the box thinking! (The differance between a machine operator and a real machinist)
Thanks, Dave. First, no problem with side tracking. In fact, it's encouraged by me, assuming it remains within the confines of the intended purpose of the board. Wonderful gems of information are often disclosed by wandering, which I find to be quite useful. The only real problem with getting off topic is that it's hard to find information in a search by title. Can't see a down side beyond that. I'm certainly not concerned with anyone "raining on my parade".

As far as the "out of the box thinking", wish I could claim this as my own, but it's nothing more than a feature offered on universal horizontal mills. It's been done before, but the setup is somewhat limited without the ability to swivel the table. Still, it offers the ability to make cuts that, otherwise, would not be possible, even with a CNC unless it has the fourth axis. I had intended to make the setup some day, which is why I jumped at the opportunity to purchase the large lot of gears I acquired many years ago, while I was still building our shop and house. Never in my wildest dreams did it occur to me that I'd have need in restoring a fine old piece of equipment.

I hope this thread encourages others to pursue similar projects. After all, that's what we're all about here!

H

Re: Milling a helix

Posted: Sun Jun 24, 2018 9:50 pm
by K. Brouwers
Hello Harold,
Did you slightly tighten the rotation locking clamp of your spacer head to prevent back lash issues when milling the slots.It would seem advantageous. Very nice. thanks for sharing.
Karel

Re: Milling a helix

Posted: Mon Jun 25, 2018 12:28 am
by Harold_V
Hello Karel!
Thanks for your comment and suggestion.
In regards to spacer head, I didn't want to alter the settings, as it's quite acceptable as is for normal use. The method I employed seemed to work adequately, and I had but one piece to make, so I just toughed it out and machined without altering the setting. I'd certainly do so if it hadn't worked, however.

I have a dividing head that goes with the tailstock I used, but I got this idea in my head and ran with it---as it gave me a little more control over concentricity than the dividing head may have. I wanted to support the shaft as near as I could to the worm, for the sake of rigidity. Gripping with the altered soft collet seemed to be the right approach, and the indexing head worked extremely well as a "spin fixture".

H

Re: Milling a helix

Posted: Mon Jun 25, 2018 12:46 am
by Harold_V
The worm was finish machined without issues. Here's a picture, including the original worm.
Worm6.JPG
There are some minor differences in the two. I didn't want to mess with the original Babbitt bearings, so I gave them a slight hone, then made the new shaft according to the resulting size. The bearing sizes are slightly larger than the original, but size doesn't matter so long as clearance is correct, and it is. Redoing the Babbitt wasn't a good idea, as they appear to have been bored on location, something that would be extremely difficult for me to accomplish, and there are no machined surfaces on the bearing housings that might facilitate a setup so they could be bored individually. Proved to be a good decision, as the shaft fits nicely.

On that subject, I made the worm tooth thicker (wider) on the replacement, to compensate for the wear in the gear. My objective was to reduce lash, and it did. As I was running blindly, I grabbed at a number that I hoped would yield success. If anything, I could have made the tooth slightly wider, but I'm well satisfied with the end results, and may even be able to limit the lash when it is assembled permanently, as the bearing blocks are somewhat adjustable, likely determined by the seals for the shaft, where it leaves the gear housing. The seals are held in an adjustable housing, so I'll play with that to achieve the best possible condition. That won't happen until the machine is assembled after painting.

The original setup had what appears to be a small problem with the thrust bearing not remaining stationary. I attributed that to the extremely narrow shoulder on which it bore, so I altered the design by adding a thrust shoulder, which now covers the majority of the bearing. That's the flange seen on the left side of the worm. The replacement bearing is somewhat different from the original, so I also altered the diameter on which it mounts, so it would be self centering. A replacement for the original bearing was still available, but I wasn't thrilled with the price. The one I chose to use cost me only about $15, while an exact replacement would have cost nearly $100. I'm satisfied with the decision to make the changes involved.

H

Re: Milling a helix

Posted: Mon Jun 25, 2018 7:03 am
by warmstrong1955
Impressive Harold!

Re: Milling a helix

Posted: Mon Jun 25, 2018 10:02 pm
by Harold_V
Thanks, Bill. I have to admit, it was a rather enjoyable project. It's been a long time since I had to dust off my old skills and produce something of necessity. There was no way I could buy this item, which would have been my first choice.

H

Re: Milling a helix

Posted: Wed Jun 27, 2018 12:14 am
by Patio
Nice job Harold! The finish looks really good in the picture.