Smithy 1220 - getting started, facing a gear, upgrades?

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Harold_V
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Harold_V »

thoraxe wrote: Thu Sep 08, 2022 3:58 pm It sounds like you are saying you want me to rotate the cutting tool HOLDER towards A, which would make for a shallower angle of attack against the interior of the gear (on the splined surface). Is that accurate?
No. Exactly the opposite. Set the tool as if you're going to take a turning cut, so you move towards B, not A. The 10° angle I spoke of would be such that the tip of the tool is closest to the face, while the heel of the tool is a small distance farther out. Experiement a little. You may find that 5° is better. That way as you face out the tool will remove material away from the tip, leaving the tip to bring the part to length. That helps limit the effect of the interrupted cut as the tool will always have a complete cut along the edge. That minimizes the hammering that is so destructive of carbide.
Should I be trying to touch the tip (X) to the splined area to cut or somewhere closer to the middle of the cutting edge (Z)? I'm assuming the tip?
Hopefully you now understand that you had the wrong impression. If the angle of the tool is shallow enough, perhaps you can see how you can actually start the cut at a point on the tool that is near to you. As you face out, the tool cuts deeper due to the angle.
Should I try to increase the RPM at all from 150? Is that too slow? Torch had suggested 500RPM.
It's hard for me to know exactly what speed might be beneficial, but I strongly recommend you stay away from 500 rpm on something this hard. As the hardness increases, the resistance to cutting produces a corresponding increase in heat, which is amplified by speed. The best indicator is the chip that comes off. It will be discolored, of that there is no doubt, but if it's coming off red, that's too fast for carbide, which will experience failure. Unlike many lathe operations, where increasing speed often pays dividends, slowing down when machining hardened objects, as well as the 300 series of stainless (excepting the free machining alloys) is generally beneficial.
Is there a better cutting tool/implement I should use here than these carbide indexed inserts?
I don't think so, not with the equipment you have at your disposal. Procedure is likely more important than tool type. The only change I'd make in your situation would be to use an insert that offered greater strength-- a parallelogram instead of a triangle, but you can accomplish the task adequately with what you're using, in spite of some saying you need to use a parting wheel. It's not that I don't think that will work, as it will, but if you want to do the job with carbide, you just have to approach the project differently. When you take the cut as I suggested, the bulk of the material is removed away from the tip of the tool, so it remains sharp longer. It takes advantage of the portion of the tool that will never, otherwise, see a cut. Why not use it?

Many, many years ago I was tasked with creating a rather large and coarse thread gauge. I had a virtually new Monarch EE at my disposal, which was used to make the needed gauge. The thread was roughed (I recall using Graphmo toolsteel), then the piece was heat treated with a target hardness of 62Rc. We did not have a thread grinder, so finish cuts were taken with the Monarch, using carbide. I found that I could take very thin cuts (a thou per pass) at an exceedingly low speed, perhaps 15 rpm. In backgear that was possible, as it had infinite speed control. The end result was satisfactory, although it would not compete with a ground thread.

I make mention of this as an example of what can be done.

One more thing. I made mention of the use of either C5 or C6 carbide. For roughing that is important, but if you get down to a tiny finish cut, you may be pleasantly surprised by the results you'd achieve with a C2 grade. It's harder than the other two but doesn't resist shock as well. I suspect that used with the angle I suggested, it may just do the job quite nicely. Worth a try if you happen to have one of the inserts.

H
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NP317
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by NP317 »

RMac's Dremel tool holder is brilliantly simple.
And my suggestion to use the grinding parting wheel is due to the lack of rigidity of the small Smithy 1220 lathe.
Otherwise, Harold speaks The Truth, as always.

Monarch lathes are rigid.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Harold_V »

NP317 wrote: Fri Sep 09, 2022 10:20 am And my suggestion to use the grinding parting wheel is due to the lack of rigidity of the small Smithy 1220 lathe.
Not having any experience with this particular machine, I have been in hopes that the methods I've suggested would help overcome the deficiencies of light duty equipment. I wouldn't be surprised if they were not successful, as rigidity is everything when machining a heat treated part. What gave me hope is that I expect the gear isn't much harder, if at all, than 50Rc. If I'm wrong in that assessment, I could easily be wrong about the process.
Monarch lathes are rigid.
Indeed! Deceptively so, especially the EE, which has just a D1-3 spindle. At a glance you'd think the machine wasn't up to much, but the degree of rigidity is extreme. That it weighs more than 3,000 pounds should be a good indicator, though.

I coveted that machine and would have purchased one readily had I had the funds. Alas, that was not to be. I simply didn't have the $10,000 needed for a new machine when I started my humble commercial shop, and that would be for a lathe without any accessories. A far cry from the price one paid later (greater than $100,000 as time wore on). Now it's too late in my life, as I'm winding down. I just have to be content to run my Sag12 Graziano, which has served me well. It's no EE, though! :wink:

H
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thoraxe
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by thoraxe »

Harold_V wrote: Fri Sep 09, 2022 1:51 am No. Exactly the opposite. Set the tool as if you're going to take a turning cut, so you move towards B, not A. The 10° angle I spoke of would be such that the tip of the tool is closest to the face, while the heel of the tool is a small distance farther out. Experiement a little. You may find that 5° is better. That way as you face out the tool will remove material away from the tip, leaving the tip to bring the part to length. That helps limit the effect of the interrupted cut as the tool will always have a complete cut along the edge. That minimizes the hammering that is so destructive of carbide.
OK, now I am confused. You had suggested cutting from the "inside out". But, if the tool is rotated towards B such that the tip is "up" and the heel is "down," I am not sure how to go from the inside out (looking at the face, center of the hole to the left towards the front of the machine).

If you look at the original post, photo #3, that appears to be exactly the orientation you are suggesting. Tip closest to face, heel small distance out. In that orientation, I was trying to face from the outside in (from the front of the machine moving the carriage towards the center axis of the gear). That brings us back to the carriage flex and nothing happened when the splined area was rubbing against any part of the carbide cutting tool but not actually cutting.

I'm not sure how I would go from the "inside out." Here's your suggestion again for reference:
Harold_V wrote: Fri Sep 09, 2022 1:51 am As you have the bulk of the material removed at this point, what I'd suggest is for you to angle the tool away from the cut with the base of the tool farther away from the face than the tip. Then take shallow facing passes from inside to outside. The gentle angle will cause greater tool contact, but the shallow cut should reduce cutting pressure and allow for easier removal of stock. By doing so, you'll reduce the effect of the interrupted cut as you remove the splined portion.
To move from inside to outside (center of gear / axis of gear towards the front of the machine) means that the "Z" mark on my annotated photo (not exactly that position) would hit before the tip (X).

Sorry for my new-ness and general confusion! I'm really just trying to understand your suggestion.

I'm not wedded to carbide or this tool. If there is a better cutting tool to do this job, I would entertain purchasing it. I have the carbide stuff because that's what was in the machine's drawer when it showed up in my garage. But, as the machine was $0 (permanent loan), I'm willing to make investments in better cutting implements -- not that I intend to cut many gears.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Torch »

thoraxe wrote: Sat Sep 10, 2022 8:29 am If you look at the original post, photo #3, that appears to be exactly the orientation you are suggesting. Tip closest to face, heel small distance out.
I think that's pretty much exactly what Harold is suggesting. Make the angle about 10° with the tip closer to the chuck. Position so the tip is inboard of the splines, and initial contact will be by the straight part of the insert, probably somewhere in line with or just beyond the screw attaching the insert to the holder.

Now draw the tool towards you as you cut (ie: inside to outside) so the meatiest and most rigid part of the tool contacts the splines first. As you draw the tool towards you, it will eventually hit the bottom of the splines so at least some of the cut is uninterrupted. This will help stabilize things so that by the time the tip is into the cut it will not receive as great a shock load. Also, while the tip will still be the furthest extent of the cut, much of the material will already be removed by the time the tip gets there.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by rmac »

thoraxe wrote: I have the carbide stuff because that's what was in the machine's drawer when it showed up in my garage
This makes me wonder about the condition of the (probably used) inserts that you have. You're going to have two strikes against you from the outset if you're using a tool that's already worn out and dull.

If you can see (using a magnifier would help) that the insert is chipped or broken, then you should obviously replace it or rotate it in the holder to expose a fresh, undamaged side if there is one.

But even if you don't see any damage, it still could be just dull and you might do yourself a favor by replacing it.

-----------------------------

Question for the more experienced guys here: How can somebody without that experience tell if a tool is is dull, given that he won't be able to subjectively observe that "it just isn't cutting right".

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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Bill Shields »

Look at the edge with a magnifier and compare to a new tool.
Too many things going on to bother listing them.
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NP317
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by NP317 »

Tool sharpness?
Look for blood on your fingers...
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Bill Shields »

Or lack of finger(s)?
Too many things going on to bother listing them.
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rmac
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by rmac »

Bill Shields wrote: Look at the edge with a magnifier and compare to a new tool.
So (I'm guessing here):

Edge looks shiny and reflective = the tool is dull

Otherwise = the tool may be sharp

Is that more or less what you're suggesting?

-- Russell Mac
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by GlennW »

Edge may be chipped or burned.
Glenn

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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Harold_V »

It is important to understand that negative rake is NOT intended to have a sharp cutting edge. That's one of the reasons why carbide isn't recommended for light duty machines. If the edge is sharp enough to cut freely, the cutting edge will readily chip, which is the beginning of the rapid end for negative rake inserts. Fact is, when negative rake was first introduced to the shop, a 5 thou chamfer was recommended to be stoned on the edge. Theory of negative rake is that the tip of the tool never touches the part, and that's quite evident if you examine an insert that has been used with adequate feed, speed and power. The chip develops well back of the tip, where minor cratering will show. That's one of the reasons shallow cuts are not recommended, as they eliminate the desired characteristics that make negative rake so advantageous.

While I can't say with certainty, it appears to me that the insert being used is negative rake, formed with a chip breaker. The edges on both sides should not be sharp. They should also not be chipped.

A positive rake tool may be to advantage, especially for a final pass. It would be far less robust, but the keen edge would perform better, as long as it was not damaged by excessive speed, the interrupted cut or the hardness. Hard to say without knowing the actual hardness of the spline, which could be exceedingly hard. I don't know if such items are nitrided, but if the gear has been so processed, the spline will be unbelievably hard to machine. Nitriding offers extreme wear resistance without sacrificing ductility, a win/win proposition where gears are concerned. While it's just a surface treatment, the geometry of a spline assures that a hard surface is always in contact with the tool. It is likely as hard as the carbide.

H
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