Newbie Looking for giddiness

This forum is dedicated to those hobbyists with the 3-in-1 metalworking machines. Mill-Drill-Lathes. Tips, techniques, modification and use of these machines is topical.

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# 1 ORF
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Newbie Looking for giddiness

Post by # 1 ORF » Thu May 03, 2012 11:43 am

Can any one describe how to cut this gear. I have a small hobby 3 in 1. and willing to learn Thanks Jim
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Torch
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Re: Newbie Looking for giddiness

Post by Torch » Thu May 03, 2012 4:56 pm

For some reason, I can barely make out your drawing -- it's very faint and very small. It looks like it might be a worm, rather than a gear? I think you can cut those in the same manner as cutting a thread. You would have to grind a form tool the right shape, and you would have to figure out the pitch and have the right gears for that pitch.

# 1 ORF
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Re: Newbie Looking for giddiness

Post by # 1 ORF » Thu May 03, 2012 7:52 pm

Torch wrote:For some reason, I can barely make out your drawing -- it's very faint and very small. It looks like it might be a worm, rather than a gear? I think you can cut those in the same manner as cutting a thread. You would have to grind a form tool the right shape, and you would have to figure out the pitch and have the right gears for that pitch.

Thanks for the replay. I've made the drawing a little bigger and darker. As you can see it can not be cut as a thread because of the stops at each end It seams to me it will have to be milled in some way. My question is how? Thanks again Jim
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Torch
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Re: Newbie Looking for giddiness

Post by Torch » Thu May 03, 2012 9:04 pm

What are you making it out of? How big is it?

No doubt it would be simple to replicate with a 4 or 5 axis CNC machine and in the past there were all sorts of mechanical gear making machines that could advance and rotate the workpiece simultaneously. But given the limitations of a 3-in-1 machine, my only thought is to mount a dremel to the tool post, then proceed as if cutting a thread.

# 1 ORF
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Re: Newbie Looking for giddiness

Post by # 1 ORF » Fri May 04, 2012 1:32 am

Torch wrote:What are you making it out of? How big is it?

No doubt it would be simple to replicate with a 4 or 5 axis CNC machine and in the past there were all sorts of mechanical gear making machines that could advance and rotate the workpiece simultaneously. But given the limitations of a 3-in-1 machine, my only thought is to mount a dremel to the tool post, then proceed as if cutting a thread.

The parts will be made from brass. will be needing two sizes 1/2" by 3/8" and 1" by 1/2. I have been thinking of mounting a high speed on the tool post and cutting it that way as you suggest. Also been thinking of building a threaded fixture to advance the part on the tool post use a cutter in the mill and turn the part by hand.????

Torch
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Re: Newbie Looking for giddiness

Post by Torch » Fri May 04, 2012 4:27 am

Yes, if you made an arbor with the same thread pitch and a female support for it to follow, that could work. You would want to fabricate a sliding support for the other end I think. You also need to be careful of backlash -- advance it to the start before plunging the cutter each time, and raise the cutter at the end of each pass before retracting it for the next one. You might be able to reduce the backlash if both supports were threaded though.

# 1 ORF
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Re: Newbie Looking for giddiness

Post by # 1 ORF » Sun May 20, 2012 3:57 pm

Fixture.jpg
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I came up with this fixture off the top of my head. Do you think this might work?. Jump in any one add your 2 cents. My program would on let me add any text on the drawing so I'm adding them here the fixture is made from 6X4X1 with 3/8-10 ACME threaded rod with hand crank. the 3/8 Brass stock is fead in on the right. The fixture will be held by a vice in the 3 in 1. Thanks for looking and for your comments. Jim :roll:

Torch
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Re: Newbie Looking for giddiness

Post by Torch » Sun May 20, 2012 5:26 pm

As long as the driving spindle is the same thread pitch (10 tpi) as your finished piece, the diameter is irrelevant -- at least in theory. I think the biggest challenge will be to control backlash while maintaining an even and constant feed rate. My gut feeling is that the larger the diameter of the driving shaft, the shallower the angle will be at a given pitch and therefore control will be better. Since standard 3/8" Acme rod is actually 12tpi and standard 1/2" Acme rod is 1/2", I think it might be not only easier to find off-the-shelf components in 1/2", it would also be to your benefit. I would also consider some sort of double-nut, perhaps with a stiff spring between, to minimize backlash. The idea is that the spring ensures the two nuts are positively engaging opposing sides of the thread.

You would need to attach your piece to your driving shaft somehow, but you can make it over-long with your preferred method of attachment in the surplus, then part it down to size and finish the ends afterwards.

If it was possible to drive it with a gear reduction, I think it would help stabilize your feed rate. Now, it may not be a big issue for you, but I find it challenging to maintain a truly constant feed rated by hand. Even using two hands I always experience some variation which shows up in surface finish. A gear (or belt, or whatever) reduction would help.

That's just my 2¢.

# 1 ORF
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Re: Newbie Looking for giddiness

Post by # 1 ORF » Sun May 20, 2012 7:41 pm

Thanks for your 2 cents. I will work on doing away with the hand crank maybe replace it with a worm drive of some kind. I'm not suer I understand your suggestion about the two nuts and spring. Do you mean to use nuts instead of threading the fixture itself ? would you elaborate on that a little. Due to the size of the drawing I did not show the detail of the Brass stock and the acme threaded rod. the acme will have a stud and the brass stock will be drilled and tap I think that will hold the two parts together. I looked in Mc Master Carr for acme stock they had 3/8-10 or 1/2-12 I will take your advice and look for a larger diameter acme. Jim

Torch
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Re: Newbie Looking for giddiness

Post by Torch » Sun May 20, 2012 10:39 pm

This is what happens when I shoot my mouth off without researching things: I didn't even know that 3/8-10 was readily available. However, looking at M-C, I don't see 1/2"-12, just 1/2-10 and 1/2-8.

Ok, for the nuts: If this is something you will be doing regularly, two bronze nuts, separated by a stiff compression spring capture the driving shaft -- really, lead screw would be a better term I guess. The outside of the nuts is fixed to the fixture with set screws or similar, after the spring is compressed somewhat between them. So one nut is pressing on the leading edge of the thread and the other against the trailing edge of the thread. This should prevent vibration that would otherwise be present from the play of a single nut.

The more the spring is compressed, the greater the resistance to backlash and the less chatter you are likely to see, BUT the nuts will wear faster and the lead screw will be harder to turn. If this is a one-off project, you could probably get away with tapping the fixture in place of one nut and using one brass nut (separated by the spring, of course) to absorb the back-lash. Bronze is better for long-term use, brass is much cheaper!

This might not be absolutely necessary, but the 3-in-1 is not the most rigid milling machine to begin with and cutting a spiral slot with a hand-cranked fixture is just going to add to the effects of vibration if there is any play in the mechanism -- I think. But I've never tried to do what you propose so I could well be wrong! Hopefully Harold or Jose will be along soon to offer the benefit of their greater experience. (Jose used to have a 3-in-1 himself, IIRC).

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Re: Newbie Looking for giddiness

Post by Harold_V » Mon May 21, 2012 12:39 am

I wish I was able to lend some thoughts to this project, but I am not able to see the part adequately, so the form of the screw is not apparent. For some reason, I can't open the second one, and the first one is too small to make any determinations.

I'm of the opinion that the screw idea has merit, in particular if the parts are to be made of brass or bronze. A snug fit of the threads to help control self feeding (hogging) is a good idea. Success may be within reach, even by hand cranking, assuming the depth of cut is reasonable.

The most critical consideration is the form of the thread, or gear tooth. Can it be described, or a larger drawing provided?

On the topic of sizes of posted drawings and pictures. The board software automatically sizes large attachments to thumbnails, which can then be clicked by readers for a larger view. That makes downloading the thread faster for folks with a dialup. A respectable sized drawing can be posted (800 pixels in width, for example) so detail is easily seen. Keep file size low, to preserve disc space on the server. A 100 kb file is generally more than large enough to provide adequate detail.

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

Torch
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Location: Muskoka

Re: Newbie Looking for giddiness

Post by Torch » Mon May 21, 2012 9:07 am

I darkened it up a bit, here's what he wants to make:
Worm .png
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