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

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

Post by thoraxe »

I inherited this Smithy 1220-XL from a friend who wanted it out of his basement. This is the first time I'm using it for a project, and I've chosen badly. I've looked through the user manual for the 1220, watched a bunch of videos on facing, and read a few things, but I'm still struggling a bit.

A friend is swapping a 5th gear in his transmission, but the one he wants to use needs to be faced down about 8mm. I'm assuming this gear is some kind of hardened steel. I've made some progress, but...

1) I'm not entirely sure what angle to approach for facing. I've tried to include a top down photo. Should I come in with more angle? Less? Is this the proper tool for the job? I'm moving from the outside to the inside which I think means I'm doing left-hand, so I think I'm actually going backwards to how the tool is facing? I included a picture of the different tip arms I have. I've already mangled a few of the tips. I'd be interested in a recommendation for a replacement tip set, or a replacement tool set.

2) I have the carriage locked, but, when I get near the interior splined area, the tip starts to vibrate and the carriage starts to flex back and forth. I'm assuming the area with the splines is way harder, and perhaps these carbide tips aren't strong enough? Does the carriage flex mean that I might need to adjust the gibs? Per #1 should I be using a different tool head and trying to start on the splines area and move from the center out?

3) I've got the speed set for 160RPM (the lowest). It's not clear if I should be going faster or not, or if I should be using a cutting oil.

4) somewhat related, when the carriage is unlocked and the engagement lever is on, the leadscrew dial moves the carriage in and out. Manually operating it also turns gears inside the machine as this is related to the power feed. I didn't see any way to completely disengage the gears. Turning the leadscrew seems to have a bit of slop. The dial is supposedly calibrated in two thousandths. I assume that going from 30-40 on this dial means I've moved 0.002"? And going from 30-35 would be 0.001"? Is there a way to clean up the slop here that seems to result from moving the gears when turning the leadscrew?

Thanks so much. I realize this machine isn't that great, and that free isn't always good. It's what I've got, though, so I'm making the best of it for now. I primarily want to use it for basic milling and drill-press operations, which I know it's even worse at. Oh well!
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Torch
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Torch »

These machines are not really the most rigid for carbide tooling. Carbide is typically ground with negative rake. You may be better off with a high quality cobalt HSS like M42 (8% cobalt) ground with a slighly positive rake. Does a file cut into it or just skate off? That will give you a rough idea how hard it is.

Carbide either wants lots and lots of coolant, or no coolant at all. Inconsistent cooling causes it to crack and chip. It doesn't care for interrupted cuts either -- the hammering also leads to chipping of the cutting edge.

At this point, assuming the gear is hardened beyond the capability of an M42 tool bit to cut, I'd consider cutting most of the spline away with a thin cut-off wheel and a grinder, then finishing the last 100 thou with a tool post grinder. Protect your bed with drop-cloths though -- you don't want abrasives getting on the ways.
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Harold_V
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Harold_V »

Torch pretty much nailed it!
If gears used in transmissions weren't hardened they wouldn't be up to the assigned task. I suspect that you're pretty much locked in to using carbide, although his recommendation to use a toolpost grinder grind is very good, assuming you have access to one, or you're acquainted with someone who owns a cylindrical grinder. It would be the best possible solution to the problem, although it would be a good idea to remove the bulk of the material before finish grinding.

I trust you have the gear properly dialed in so the resulting face will be parallel with the back side.

Handing a cutting tool for a lathe doesn't make a lot of sense, but it is accomplished by holding the tool in front of you with the cutting tip up, and the shank pointing away from you. The direction the cutting edge points is the hand of the tool. In this case, based on the third picture, that's a right-handed tool, not a left.

The insert tool you've chosen isn't the best choice, although it's capable of doing what you're doing. It appears your choice is to take successive passes instead of facing away the material. Shallow cuts are in order, and you should expect compromised insert life and performance. The grade of carbide is critical ---I suspect a C5 or C6 grade will yield the best service.

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.

A sharp insert for finish passes is recommended, as is a light cut (shallow in depth).

You've chosen a tough project on which to learn. After this experience, you'll find machining annealed materials a breeze.

Welcome to the board.

H

Edit:
One thing I should have mentioned. With a sharp insert, if the cut generates and sparking, slow down. Chips will come off hot, maybe even dull red, but if they come off hot enough to spark, tip failure isn't far away unless you're using a ceramic insert, which would be a poor choice for the interrupted cut.
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thoraxe
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by thoraxe »

Torch wrote: Mon Sep 05, 2022 10:17 pm These machines are not really the most rigid for carbide tooling. Carbide is typically ground with negative rake. You may be better off with a high quality cobalt HSS like M42 (8% cobalt) ground with a slighly positive rake. Does a file cut into it or just skate off? That will give you a rough idea how hard it is.
I took a regular hand file, one that's not crazy aggressive but definitely not smooth, and put the gear in a benchtop vise to try to see what would happen. It didn't seem like it did much of anything. I don't have the right tool (read: benchtop grinder) to make a custom-ground HSS.
Torch wrote: Mon Sep 05, 2022 10:17 pm Carbide either wants lots and lots of coolant, or no coolant at all. Inconsistent cooling causes it to crack and chip. It doesn't care for interrupted cuts either -- the hammering also leads to chipping of the cutting edge.
Copy that.
Torch wrote: Mon Sep 05, 2022 10:17 pm At this point, assuming the gear is hardened beyond the capability of an M42 tool bit to cut, I'd consider cutting most of the spline away with a thin cut-off wheel and a grinder, then finishing the last 100 thou with a tool post grinder. Protect your bed with drop-cloths though -- you don't want abrasives getting on the ways.
Tool post grinders seem to be rather pricey. At that point, I might just take the gear to a local machine shop - there are quite a few.

Thank you for your thoughts!
thoraxe
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by thoraxe »

Harold_V wrote: Tue Sep 06, 2022 1:44 am Torch pretty much nailed it!
If gears used in transmissions weren't hardened they wouldn't be up to the assigned task. I suspect that you're pretty much locked in to using carbide, although his recommendation to use a toolpost grinder grind is very good, assuming you have access to one, or you're acquainted with someone who owns a cylindrical grinder. It would be the best possible solution to the problem, although it would be a good idea to remove the bulk of the material before finish grinding.
I would buy other lathe tools if they were reasonably priced. Any significant investment likely isn't worth it, as I doubt I'd ever do this again and I have access to many machine shops in my area that could do this for the price of the "right" tool. So, it's a wash. Then again, the friend whose gear it is might buy me the tool in exchange for the work, so...
Harold_V wrote: Tue Sep 06, 2022 1:44 am I trust you have the gear properly dialed in so the resulting face will be parallel with the back side.
I've got the back face of the gear jammed against the chuck and biting on the same collar on the back side of the gear. So, my grinding/facing is roughly parallel with the face of the gear, assuming the gear's back and front faces are parallel to one another. That being said, the gear is located on the shaft by the splines, and the orientation is set by the splines, not the faces. Yes, I want to be as close to parallel on everything as possible, but I get the sense some misalignment here may not be a problem.
Harold_V wrote: Tue Sep 06, 2022 1:44 am Handing a cutting tool for a lathe doesn't make a lot of sense, but it is accomplished by holding the tool in front of you with the cutting tip up, and the shank pointing away from you. The direction the cutting edge points is the hand of the tool. In this case, based on the third picture, that's a right-handed tool, not a left.
The video (which I can't find the link for) mentioned that the "handing" of the facing operation had to do with the direction that the tool moved across the face, when looking at the face. A "right-handed" facing would be when the tool is moving from left-right along the face. A "left-handed" facing would be when the tool is moving from the right to the left across the face. But, to your point, in this scenario (facing) it doesn't make a ton of sense. In other scenarios, it likely does.
Harold_V wrote: Tue Sep 06, 2022 1:44 am The insert tool you've chosen isn't the best choice, although it's capable of doing what you're doing. It appears your choice is to take successive passes instead of facing away the material. Shallow cuts are in order, and you should expect compromised insert life and performance. The grade of carbide is critical ---I suspect a C5 or C6 grade will yield the best service.
Yes and no. I mostly attempted to remove what I could and left the parts that seemed sketchy -- the splines. The main meat of the gear I was able to remove 1-thou at a time along the gear. I've almost got everything removed down to the target depth. But the splined area remains troublesome.
Harold_V wrote: Tue Sep 06, 2022 1:44 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.

A sharp insert for finish passes is recommended, as is a light cut (shallow in depth).

You've chosen a tough project on which to learn. After this experience, you'll find machining annealed materials a breeze.

Welcome to the board.

H

Edit:
One thing I should have mentioned. With a sharp insert, if the cut generates and sparking, slow down. Chips will come off hot, maybe even dull red, but if they come off hot enough to spark, tip failure isn't far away unless you're using a ceramic insert, which would be a poor choice for the interrupted cut.
Is the attached photo showing the orientation you are describing? I attempted to use this, moving the edge of the cutting tool (not the tip) towards the splines from the center of the gear until it touched. Once the edge of the cutting tool hit the splines, it did nothing. It just vibrated a bunch. As I tried to move the carriage more, the tool cut nothing, and then the carriage started to flex a bit. I didn't want to apply too much pressure because I was afraid of either the spline "catching" the tool edge and either locking up (crashing?) or breaking/chipping another insert. It seems that these items may be roughly the same hardness (the tool and the spline material). My guess is that I need a harder/sharper tool.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Torch »

The carriage flex is exactly what I mean when I say these machines are not really rigid enough. You won't find tooling harder than carbide, but the machine has to be rigid enough and powerful enough to push the carbide into the material.

The other thing to remember is that there is a trade-off between hard and tough. And by tough, I mean the opposite of brittle. Yes, there are certainly different classes of steel, but in general the harder you make a given steel, the more brittle you make it. That's why carbide tends to chip on an interrupted cut and why carbide tools are not sharpened to a keen (thin) edge with positive rake -- they need more material to be adequately strong. They have more of a scraping action than a cutting action.

If you are going to try the setup shown from inside to out, then I would suggest taking very shallow passes -- perhaps 0.010" -- and bump the speed up to somewhere around 3-400 rpm (I'm guessing that piece is around 1-1/2" or so?) with a firm feed rate. And be prepared to change inserts regularly. (But if Harold says otherwise, then do what he says. He's a lot better at this stuff than I am.)
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Torch »

Oh, and you don't have to buy a $4,000 toolpost grinder. Little Machine Shop has a few hobby-class versions for ~$200. Some guys have built them with little more than an old router. I have a die grinder I can mount to the tool post.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by NP317 »

And many hobby machinists have mounted Dremel (or similar) tools as small grinders.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by Harold_V »

thoraxe wrote: Tue Sep 06, 2022 8:11 pm The video (which I can't find the link for) mentioned that the "handing" of the facing operation had to do with the direction that the tool moved across the face, when looking at the face.
Handing of a tool has nothing to do with the direction it is used (although it is often related to its function). It's to do with the tool geometry. A right hand tool is always a right hand tool, even when used for other functions.
Harold_V wrote: Tue Sep 06, 2022 1:44 am The insert tool you've chosen isn't the best choice, although it's capable of doing what you're doing. It appears your choice is to take successive passes instead of facing away the material. Shallow cuts are in order, and you should expect compromised insert life and performance. The grade of carbide is critical ---I suspect a C5 or C6 grade will yield the best service.
thorax wrote:But the splined area remains troublesome.
Modern technology allows for induction heat treating of such items. The spline is likely harder than the body, as would be the teeth. By selectively heating the desired surfaces, a more robust and reliable component is created.
Harold_V wrote: Tue Sep 06, 2022 1:44 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.
"thoraxe" wrote: Is the attached photo showing the orientation you are describing?
Not exactly. Note the comment about the "gentle angle", which is everything in this case. If numbers might help, I'd suggest something like 10°. It's not carved in stone, as various angles will produce acceptable results. By facing in to out, the side of the tool will remove the material, leaving the tip to establish finished length. The gentle angle cuts down on the troublesome part of machining an interrupted cut that is heat treated.
"thoraxe" wrote: It seems that these items may be roughly the same hardness (the tool and the spline material)
Not even close! I suspect that the hardened gear is in the vicinity of 50Rc, while tungsten carbide tends to run above 70Rc. That doesn't really represent the actual hardness of the carbide, as it's a fused product. The reading is an average of the bonding agent and the tungsten carbide of which the tool is made. That said, hardened materials resist cutting and are correspondingly difficult to machine as hardness increases. Ceramic inserts tend to overcome the hardness problem, although with limited depths of cut and they do not respond well to interrupted cuts. Their use demands extremely rigid equipment and adequate power, otherwise they simply self destruct.

A comment about my concern for parallelism. The gear in question is a helical gear, which means that it yields thrust when under power. If the shoulder you create isn't perpendicular to the gear, the slight area that behaves as a bearing has the potential for premature wear, possibly resulting in failure. While it's true that the spline/shoulder/teeth are the critical features, keep in mind that parts such as this must be handled time and again in the process of being made. You can usually safely assume that the features will be related to the major diameter as well as the faces. Otherwise they would be difficult to orient when they are moved from one operation to another. That may or may not be true in all cases, however.

Just sayin'

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

Post by thoraxe »

Thanks so much for the response. I'm still a little confused, so I attached an annotated image.

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?

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?

Should I try to increase the RPM at all from 150? Is that too slow? Torch had suggested 500RPM.

Is there a better cutting tool/implement I should use here than these carbide indexed inserts?
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by NP317 »

I would not attempt to cut the spines with that tool. I don't see any way of success with the intermittent cut of hardened steels.
That carbide insert will break.
I would follow others' suggestions to cut through the splines with an abrasive cutting tool.
Even a Dremel tool could work. I have done exactly that with success.
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by rmac »

NP317 wrote: I would follow others' suggestions to cut through the splines with an abrasive cutting tool. Even a Dremel tool could work. I have done exactly that with success.
NP317 wrote: And many hobby machinists have mounted Dremel (or similar) tools as small grinders.
Depending on what you're starting with, mounting a Dremel on the tool post doesn't have to be a huge project, either. I got away with a simple chunk of aluminum with a threaded hole to match the nose of the Dremel.

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