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

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

Post by rmac »

Harold_V wrote: It is important to understand that negative rake is NOT intended to have a sharp cutting edge.
... and ...
Harold_V wrote: The edges on both sides should not be sharp.
Harold, are you saying here that I was off base earlier when I was wondering if thoraxe's tool might be worn out from prior use? If so, I'll happily edit or delete that post. I sure don't want to confuse anyone with bad information.

Aside from that, can you explain what you mean above by "both sides"? Both sides of what? That's not clear to me.

Thanks,

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

Post by Harold_V »

rmac wrote: Sat Sep 10, 2022 9:37 pm
Harold_V wrote: It is important to understand that negative rake is NOT intended to have a sharp cutting edge.
... and ...
Harold_V wrote: The edges on both sides should not be sharp.
Harold, are you saying here that I was off base earlier when I was wondering if thoraxe's tool might be worn out from prior use?
Absolutely not! But knowing what's wrong with a cutting edge becomes important. In my experience, when a negative rake insert gets used as intended, it breaks down where the outer portion of the cut makes contact with the tool (the edge degrades at that interface]. Once that starts happening, there's a rapid degradation of the tool's performance, and if one persists, the end result is often a broken insert. This condition is common when multiple parts are being roughed with the same depth of cut per pass. The tip of the tool may be in acceptable condition, and the cutting edge may, otherwise, still look good. If a shallower depth of cut is taken, the tool may perform acceptably.
I sure don't want to confuse anyone with bad information.
That's noble, as some don't care, so long as they are heard.

When I try to evaluate a negative rake insert, what I look for is chipping, wear, and/or cratering of the insert. Those features are quite obvious if compared to a pristine insert. If there's any indication the cutting edge has been chipped, I make a decision on taking a risk of getting a few more miles from that particular tip, or to index to a different one, known to be in acceptable condition. If I find that all corners on both sides have minimal damage and the insert is of little value, I often will pick the best tip and use it for heavy roughing. I'll risk breaking the insert because it's no good anyway.

The typical negative rake insert is NOT ground. They are generally dispensed as they are made, and it shows if you know what you're looking for. That usually results in dull (not sharp, but smooth and very regular in appearance) edges, which are far less important in negative rake as compared to positive rake inserts. Remember---a negative rake tool is NOT intended to cut at the tip.
Aside from that, can you explain what you mean above by "both sides"? Both sides of what? That's not clear to me.
Sorry. I should have been a little more explicit. By both sides, I mean both top and bottom faces of the insert.
The typical (negative rake) triangular insert offers six cutting tips, three on each side. That's not typically true of positive rake inserts, where rake is created by tilting the insert, which, in doing so, creates negative clearances. That necessitates front and side clearance must be ground on the insert, so the use of both top and bottom is not possible. By sharp contrast, if a positive rake insert is ground from a negative rake insert (commonly done), the tool holder itself creates the required clearances, so both sides of the insert can be used. Such inserts are far better suited for finish cuts and perform poorly for roughing.

If folks are hell bent on using carbide inserts, they should become familiar with the differences in inserts and holder so the choices they make are in keeping with their needs. Grabbing a random holder isn't in anyone's best interest, assuming they are trying to solve a given problem.

I often get on my soapbox and try to encourage folks to learn how to grind their own tools. The knowledge gained is priceless, as once one understands the geometry involved, it's dead easy to see what's wrong with a cutting edge---and offers one the ability to correct less than acceptable geometry. I like to say that a lathe man is held captive as long as he's unable to fashion his own cutting tools. It's true! :wink:

Our GlennW is well versed on this subject. His comments should override mine, as my distance from the production shop for so many years has left me lacking a great deal of knowledge. Much of what I speak was acceptable 40 years ago, but much has changed in that time, including the introduction of micro-grain carbide, along with improved bonding techniques. The carbide of today is a far cry from that which was in common use in the 70's.

Glenn also has some experience with Cermet inserts, which are very good for machining hardened materials. Perhaps he could offer some guidance.

H
Wise people talk because they have something to say. Fools talk because they have to say something.
thoraxe
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by thoraxe »

Harold_V wrote: Sat Sep 10, 2022 11:42 pm 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?
Amazon has an amazing selection of (probably garbage) indexed tools and tips. Smithy appears to be out of stock on their own inserts:
https://smithy.com/products/tin-coated- ... 4360013889

I do have several more triangle inserts that all appear to be unused.

I assume that these inserts are relatively standard. However, you had recommended a parallelogram insert, so that would mean a different tool/holder. Again, I'm happy to buy a better/right tool for this job, especially if it would improve all other jobs down the line. I took a quick spin in the lathe forum to see if there were strong recommendations, but I did not find any definitive link or supplier mention. I am happy to buy a proper indexable set from anywhere. I had poked around on the McMaster Carr site but was stymied by the sheer number of options and the high prices for even individual holders. I have a guess they're not the best choice of supplier for the casual home machinist.

There's something like this which includes parallelogram holders as well as a few other holders/tools that I do not currently have:
https://amzn.to/3BwJjoP

The above is not C2 grade, though. It does look similar to the Grizzly kit but for $50 less:
https://www.grizzly.com/products/grizzl ... 1-2/t10294

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

Post by Harold_V »

I would caution you against one thing. Years ago, when I resided in Utah, a fellow club member asked me to stop by to see why the insert tooling he had purchased didn't work as he hoped. Keeping in mind that I do not bad-mouth things made in China simply because they're made in China, what I discovered was that the insert holders he had purchased had the proper configuration pocket for the inserts, but they were machined without the required rake angle, so the insert, when installed, had no clearance. It would not perform its intended duty. The holders were nothing short of scrap metal.

If you pursue any new holders, ensure that they are properly made, that the insert used is set in the proper attitude so it offers the ability to take a cut. His did not. It is difficult to judge from photos alone unless they provide an exploded view of the pocket and how it relates to the shank.

Due to the indexable square block I use on my Graziano (by choice), I am limited to ½" shank tooling. That's not a problem with HSS cutting tools, but for carbide insert tooling it certainly can be. They are rather fragile due to the small insert that is required. Rather than fight with limited strength inserts, I tend to use larger shank tooling, which steps up to larger inscribed circle inserts. I do that by milling down the bottoms of the larger holders to bring the cutting tip down to the centerline of the lathe. It must be done only once, then a holder that is far more useful is at one's disposal. I'm not suggesting you do that but do keep it in mind if you are struggling with the breakage of the much more fragile small inserts.

One thing I highly recommend. Concentrate on learning to grind your own tools (HSS). Not because it's a solution for the current problem, for it isn't. If you learn how to grind a proper tool, you'll then be able to judge what's wrong with other tools and be able to make decisions that are meaningful. Until you can do that, you're going to find yourself held hostage by your lack of knowledge.

I realize that's not what you want to hear. That doesn't change the fact that it's true!

H
Wise people talk because they have something to say. Fools talk because they have to say something.
thoraxe
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by thoraxe »

Harold_V wrote: Sun Sep 11, 2022 4:29 pm I would caution you against one thing. Years ago, when I resided in Utah, a fellow club member asked me to stop by to see why the insert tooling he had purchased didn't work as he hoped. Keeping in mind that I do not bad-mouth things made in China simply because they're made in China, what I discovered was that the insert holders he had purchased had the proper configuration pocket for the inserts, but they were machined without the required rake angle, so the insert, when installed, had no clearance. It would not perform its intended duty. The holders were nothing short of scrap metal.

If you pursue any new holders, ensure that they are properly made, that the insert used is set in the proper attitude so it offers the ability to take a cut. His did not. It is difficult to judge from photos alone unless they provide an exploded view of the pocket and how it relates to the shank.

Due to the indexable square block I use on my Graziano (by choice), I am limited to ½" shank tooling. That's not a problem with HSS cutting tools, but for carbide insert tooling it certainly can be. They are rather fragile due to the small insert that is required. Rather than fight with limited strength inserts, I tend to use larger shank tooling, which steps up to larger inscribed circle inserts. I do that by milling down the bottoms of the larger holders to bring the cutting tip down to the centerline of the lathe. It must be done only once, then a holder that is far more useful is at one's disposal. I'm not suggesting you do that but do keep it in mind if you are struggling with the breakage of the much more fragile small inserts.

One thing I highly recommend. Concentrate on learning to grind your own tools (HSS). Not because it's a solution for the current problem, for it isn't. If you learn how to grind a proper tool, you'll then be able to judge what's wrong with other tools and be able to make decisions that are meaningful. Until you can do that, you're going to find yourself held hostage by your lack of knowledge.

I realize that's not what you want to hear. That doesn't change the fact that it's true!

H
Totally understood regarding grinding my own HSS. At some point, I will get a welder which means there'll be two uses for a quality grinder, at which point it might make sense to get one. However, at present, none of that is in the cards.

I attempted to cut the splines at a shallower angle (~10deg measured using a phone app, close enough). I also pushed on the carriage while moving it onto the workpiece to prevent some flex. I was able to shave a tiny bit of the splines off, but the tool eventually got chipped. I just don't think I'll be able to get this job done with this particular 3-in-1 without a dramatically different tool or approach. Oh well -- my buddy will take it somewhere to have it done/finished properly.

I'll start a separate thread for tool recommendations. Thanks for all the help!
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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: Mon Sep 12, 2022 7:21 am At some point, I will get a welder which means there'll be two uses for a quality grinder, at which point it might make sense to get one. However, at present, none of that is in the cards.
Understood, but don't fall in to the trap whereby you think a grinding wheel is a grinding wheel and can be used across the board. That will lead you to more frustration. HSS requires a soft wheel that isn't suited ***at all*** for grinding mild steel. A grinder that is intended for use in welding isn't even remotely similar to one used for sharpening HSS---although all too many do so.

Again, "just sayin'"

H
Wise people talk because they have something to say. Fools talk because they have to say something.
thoraxe
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Re: Smithy 1220 - getting started, facing a gear, upgrades?

Post by thoraxe »

Harold_V wrote: Tue Sep 13, 2022 1:46 am Understood, but don't fall in to the trap whereby you think a grinding wheel is a grinding wheel and can be used across the board. That will lead you to more frustration. HSS requires a soft wheel that isn't suited ***at all*** for grinding mild steel. A grinder that is intended for use in welding isn't even remotely similar to one used for sharpening HSS---although all too many do so.

Again, "just sayin'"

H
I read that post :wink:

The grind-ER and the grinding WHEEL are different things. One is the machine that spins the other. A quality grind-ER with the right wheel will do the job. Right? Now, if it's a monstrous pain to change the wheel to grind HSS, well, that's a different story.

BTW my grinding wheel use in welding is for the welder tips (eg: Tungsten TIG tips)
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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: Tue Sep 13, 2022 11:18 am BTW my grinding wheel use in welding is for the welder tips (eg: Tungsten TIG tips)
Got it! I use mine the same way. The tungsten is hard on the wheel, but it works adequately. Aluminum oxide isn't the best possible choice for that purpose. If I did more welding, I'd likely procure a dedicated grinder, but welding, for me, is very sporadic. Not worth the effort or lost space.

You alluded to having read my old comments, so you likely understand that it's not easy to find a suitable wheel that mounts on a bench or pedestal grinder fur use in grinding HSS. That's why I made adapters so cutter grinder/surface grinder wheels can be installed. They typically come with 1¼" bores and are available in a much greater variety of abrasive and bond types, as well as a wide range of hardness. I repeat myself here in case others may not be aware.

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