Milling a helix

Discussion on all milling machines vertical & horizontal, including but not limited to Bridgeports, Hardinge, South Bend, Clausing, Van Norman, including imports.

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Harold_V
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Milling a helix

Post by Harold_V » Mon Jun 04, 2018 1:16 am

I have a multitude of projects I'm trying to address, so I can get my shop fully operational. It's a daunting task, with some things necessary before others, so I don't paint myself in to a corner. Getting my muller operational is one of those things, which must be rebuilt and placed before I set the two furnaces for my induction melting system. I don't have excessive space, so things will be snug, with the two furnaces precluding access to the muller with my fork lift.

That said, I dismantled the muller for cleaning and rebuilding some time ago. I've made new axles for the rollers, which I made 1/16" oversized, which then allowed me to rebore the original bronze bushings for a proper fit. The wheels mount on an overhead arm, which was honed to restore the bores, and new shafts made. The mounting end is square, and required re-machining, as the muller had been somewhat abused and neglected, with the arms operated without the mounting bolt firmly tightened, resulting in worn attaching points. It is all like new now, and should work well for a long time to come.

I was feeling pretty good about the restoration project, but when I got down to the transmission, which is a simple worm/gear assembly, I found that water had entered the oil, resulting in a badly pitted worm, but only where it was submerged in the oil, which, now, was rather viscous.

I contacted Simpson, the maker of the muller, and discovered the machine was built in 1947, and sold to the University of Utah. That all made sense, for I knew it was old, and it was purchased by me from their surplus sales about 25 years ago. Like the induction furnace, it was placed in storage until the day came when I could attempt to make it operational.

Simpson was wonderful, once I reached the CEO. The parts department didn't address my inquiry, so I chanced sending a message to him to see if I could learn more. It was he who told me about the original buyer, and when it was built, and he answered the question about the lack of response from their parts department. The company had scrapped all the files prior to 1950, thus they were not able to help.

That left me with the need for a new worm, which is integral with the shaft, and is a bastard. There is nothing on the market that could substitute, so I pondered the idea of regrinding the worm, which I could do with a gearing setup, using my cutter grinder, if only the head could be tilted to parallel the helix angle. It can not.

I started thinking about making a new one, but the worm is akin to a 29° Acme thread, with a lead of 5/8" (the screw advances 5/8" per revolution). As my Graziano is way too small to accommodate that kind of pitch, I started thinking about cutting the worm on my Bridgeport. A simple gearing setup would allow the generation of the helix, with the added advantage of not requiring a form cutter, as the head can be tilted to 14°30' so each face can be machined individually. Convinced I could use Stressproof for material, eliminating the heat treat, I decided to build the required attachment.

When an old buddy closed his shop a few years ago, I was gifted his supply of material. Included was a nice piece of 3/4" aluminum tooling plate, about 23" square, although it had been used as a base plate for what was likely a CNC. No matter, it would still serve the purpose, and the price was right. I just have to live with the odd hole that makes no sense, and the slots that were already milled in the plate. Most of them are hidden by making that face the bottom.

I began the build by inspecting the left hand side of the table, where I had, long ago, removed the handle. I don't operate my mill from that postion, and I didn't like it twirling when I was using power feed. It didn't take but a few seconds to realize that I could make an adapter that fit where the handle did, and it would be driven by the same key slot that drove the handle. I went to my collection of gears, of which I have about 150. I found I had several 54 tooth gears, which would work perfectly for the application at hand. I made the adapter, then I started with the aluminum tooling plate. I wanted to be able to place the power takeoff on the machine without hassle, so I made a pair of pins that locate the adapter plate square, with the left side pin also acting as a stop, so the plate is properly oriented with the gear on the end. I then made the base plate and vertical plate, determining locations of slots as I progressed. None of this was drawn up---it was built according to what appeared to work as I'd place pieces on the plate.

In order for the power takeoff to be reversed, I cut a slot that would allow the addition of a fifth gear. It is unused, as the device appears to be operating in the proper direction for the given application.

In order for a telescoping drive to be used (one has no idea how long the connecting shaft must be for any given setup), I used a socket that has a U joint as part of its design. The socket is 3/8" drive, and will accommodate 5/16" square material, which I will use as part of the telescoping drive shaft. I also happened to have a 5/16" square holed sleeve, which will be silver soldered inside a piece of 3/8" pipe.

I was fortunate to find a pair of the sockets, each different, and each perfectly suited to the application, in the toolbox I acquired when I married my wife those many years ago. Her first husband, who was just a lad of 23, was killed in a collision while on a weekend drill in the Utah Air Guard. He had worked as a diesel mechanic, so he had some very nice tools.

In order for the socket to be mounted, I had to drill and tap for a set screw in each half. I figured sockets were heat treated, which they are, but the one thing I didn't count on was that they might be nitrided, but that turns out to be the case. I tried dimpling the socket with a center drill, only to see the tip of the center drill quickly be rubbed away. Not to be deterred, I figured if I could get through the exterior, I could probably drill and tap with little trouble, and that proved to be the case. I selected a couple scrap pieces of round carbide, from which I quickly ground a couple spade drills. Size was not important, all I needed to do was get through the skin with a larger diameter than the tap (10-32) I'd use. I was amazed to see the carbide walk right through the skin, in spite of my careless grinding, which was offhand with no particular attention paid to center or uniformity.

Long story short, I now have that portion of the setup operational. I still have to make a base plate for the holding device, which will be an unmatched tailstock and my Hardinge index head, as well as a second gear plate, which will allow power to be transferred to the worm I intend to mill. I've included the worm/shaft in both pictures, to give you an idea of what I'm talking about.

I'll try to post on my progress at some future date, maybe even include a picture of the entire setup, in use, but for right now I thought you guys might like seeing how a gear setup can be built that allows for creating helixes on a milling machine.

H
Attachments
Bridgeport power takeoff2.JPG
Bridgeport power takeoff1.JPG
Wise people talk because they have something to say. Fools talk because they have to say something.

earlgo
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Re: Milling a helix

Post by earlgo » Mon Jun 04, 2018 8:26 am

Very innovative, Harold. I see that you made the gear pivots adjustable in case you have to do this again sometime for a different pitch, etc.
Nice job.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.

RSG
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Re: Milling a helix

Post by RSG » Mon Jun 04, 2018 9:27 am

Well isn't that slick! I love some of the ingenuity found here from the members!

Lets see more pics Harold!
Vision is not seeing things as they are, but as they will be.

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Dave_C
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Re: Milling a helix

Post by Dave_C » Mon Jun 04, 2018 11:09 am

Well isn't that slick! I love some of the ingenuity found here from the members!
And more to the point, most of the really good stuff I've learned in life I learned from someone older than me. Older people know stuff because they've been there and done it!

That is a very well thought out solution Harold.

Dave C.
I learn something new every day! Problem is I forget two.

Harold_V
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Re: Milling a helix

Post by Harold_V » Mon Jun 04, 2018 10:10 pm

earlgo wrote:
Mon Jun 04, 2018 8:26 am
Very innovative, Harold. I see that you made the gear pivots adjustable in case you have to do this again sometime for a different pitch, etc.
Correct! It wouldn't make much sense to build this without future use In mind, as it is rather labor intensive. Haven't had to spend a dime so far, as it's built with material I have on hand.
Nice job.
Thanks. While I was working on the project, it took me back to the years when I was building tooling. It was very comfortable for me in a strange way. I was really happy to get off the machines when I closed the doors to my shop back in '83, but I'm finding pleasure, now, in having the equipment, as it is solving many of my needs.
That is a very well thought out solution Harold.
Thanks, Earl. I prepared for this project long ago when I was offered the huge array of gears I purchased, precisely with this project in mind. I had no idea if or when I'd need the setup, but figured it would be quite nice to have. I had little idea that I'd be faced with the project of making the worm, and would be hard pressed to create it without the setup.

Part of the trouble with machining a coarse lead like that which is required is that most small lathes can't be slowed enough to cut the thread, let alone to create the required lead with the built in gear train. Imagine how fast the carriage would be moving with that lead. By milling, all of that changes. Speed is no longer an issue.

I'll know better how this shakes out as I progress, but in the mean time, today I received the 32" (2-1/8" Ø) length of Stressproof I purchased. I did due diligence in pursuing an acceptable price, and was shocked at the disregard for small orders I experienced. I thought I had hit a winner when I was quoted $143 and change for the piece, but cut from 2¼" bar, but realized I was still being charged a high price, especially considering that did not include shipping. I inquired of a shop owner in Centralia where one might be able to purchase small lots of steel at a reasonable price and was given the name of a supplier in Portland, Oregon. A phone call on their toll free line rervealed a reasonable price, so the material was ordered. It was purchased for just under $98, including shipping, which was near $30 alone. Goes to show, there are still some companies interested in your business.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Harold_V
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Re: Milling a helix

Post by Harold_V » Mon Jun 04, 2018 11:52 pm

RSG wrote:
Mon Jun 04, 2018 9:27 am
Lets see more pics Harold!
Anything particular? I'm happy to comply, but I didn't want to post a bunch of things that others might not find of interest.
I do plan to show the entire setup, in use, when it's finished. I still have quite a bit to build, so it won't be for a few days, maybe even a couple weeks. Lots to do, and I'm spread thin. I never thought being retired would keep me so busy. :D

H
Wise people talk because they have something to say. Fools talk because they have to say something.

Jerry_H
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Re: Milling a helix

Post by Jerry_H » Tue Jun 05, 2018 12:41 am

Yeh, how did we get it all done when we worked for a living ??

Jerry
www.chaski.com

JackF
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Re: Milling a helix

Post by JackF » Tue Jun 05, 2018 4:14 pm

Another "Nice Job" Harold. I too would like to see it in action. :) When i was still in Wa. and a member of an informal hobby machinists group one of the guys needed to make a helix cut in a piece of tubing and we "worried" how to do it without a CNC machine. Now I can see how it could be done on the mill. A pic of the cutter you made would be nice too.


Jack.

Harold_V
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Re: Milling a helix

Post by Harold_V » Wed Jun 06, 2018 3:49 am

JackF wrote:
Tue Jun 05, 2018 4:14 pm
Another "Nice Job" Harold. I too would like to see it in action. :) When i was still in Wa. and a member of an informal hobby machinists group one of the guys needed to make a helix cut in a piece of tubing and we "worried" how to do it without a CNC machine. Now I can see how it could be done on the mill.
The setup I've made is quite common for a universal mill, which allows for the table to be swiveled. The machines used are generally horizontals, so side cutters can be employed. It's not common to see plain mills with this type of setup, as they're relatively restricted. In order for me to create the proper thread form, I must be dead on center, and the cutter used must be either an angular end mill, using it with the head dead true, or an end mill, offsetting the head to create the required angle of the worm. Different types of cutters (think Woodruff key, or any type side cutter) could be used by machining on either side, typically on center, however, but the form I require can't be machined without setting the side cutter at the helix angle (which is what the universal mill allows). In other words, a side cutter can't be employed, so cutting things like helical gears doesn't work. Still, options that are not at one's disposal without this setup become possible, as this job proves.
A pic of the cutter you made would be nice too.
Fortunately, because the head of a Bridgeport is capable of tilting to the side, and the depth of cut isn't beyond reason, I won't use a special cutter, although my first thought was to do so. It isn't necessary, and there's a huge benefit in just using a straight end mill, which, in my case, will be 3/16" diameter. I'll probably rough the entire "thread" by starting with the spindle vertical. That will permit me to mill to full depth, with little regard to the finish of what will become the flanks, as they will each be further machined by tilting the head 14°30'. I'll have to tilt the head to the opposite side for the opposing flank, as the setup I'll make will include a 100 tooth gear installed on one end of the worm, which will be machined oversized to accommodate the gear. That will make reversing the part in the setup impossible, but that's not an issue, as the opposing flank, in theory, will never touch the gear, so if I happen to miss the angle by a few minutes, no harm done. Setting the angle is the real challenge, as marks on machines are not accurate enough to be reliable.

I've used end mills with angles ground on them, primarily for making ingot molds when I was refining precious metals. I'm not all that keen on their use, which is another reason I chose to use straight end mills, which will be far more economical. I'll rough with HSS, but will use carbide for finish passes, so I can achieve a respectable finish on the worm. I hope to limit the amount of polishing it will require, as finish is critical, to limit wear on the bronze gear.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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GlennW
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Re: Milling a helix

Post by GlennW » Wed Jun 06, 2018 6:48 am

Harold_V wrote:
Wed Jun 06, 2018 3:49 am
Setting the angle is the real challenge, as marks on machines are not accurate enough to be reliable.
Sweeping an accurately positioned sine plate or bar with a DTI in the spindle should be plenty accurate. No?
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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Dave_C
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Re: Milling a helix

Post by Dave_C » Wed Jun 06, 2018 7:53 am

Getting my muller operational is one of those things
Any chance of showing us a picture of what a Muller is? I'm thinking it has some use in the melting/casting work but I've never been around any of that to know what you are speaking of.

Just curious..

Dave C.
I learn something new every day! Problem is I forget two.

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NP317
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Re: Milling a helix

Post by NP317 » Wed Jun 06, 2018 9:11 am

Picture a large kitchen bread-dough blender, but for sand. Usually wider than deep, with slow moving mixing blades.
Many variations of design are possible. Even a cement mixer can work nicely.
~RN

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