Re: Carbide - Surface Finish - 9A


Bill in OKC too
 

I understand your concern! It depends on what you have. Some carbide is made a bit sharper than other carbide, but carbide is granules of very high-carbon material in a softer metal binder. The granules are usually some sort of crystal, so they may have sharp edges, but those don't necessarily present at the cutting edge of the tool. Grinders that are made for sharpening carbide tooling usually have diamond grinding wheels, but they may not be the finest grain. 

Personally, I use an Eze-Lap Super fine diamond hone on my HSS cutters, and cheap chinese import carbide inserts in cheap insert holders, so haven't worried about honing them. My home machines aren't large or heavy enough to take best advantage of carbide tooling. Your 9A is probably a better machine than my 10" TH42, but neither of them are super stiff. 

If you have a 10X loupe or magnifier, you can look at the edges and select inserts that seem to be sharper for your finish work. Carbide is mostly used in production shops to get maximum productivity in minimum time on heavy machines. You won't be able to take full advantage of it on the lighter machines, but you can do good work within the limits of machine. 

There are different grades and materials used in the inserts that work better for certain materials, and if you can identify what you have you can take advantage of those differences, but if they they're unmarked you'll just have to guess, and hope it works out. Carbidedepot.com used to have some really good info on selecting carbide inserts, but their site doesn't seem to be working anymore in the Brave browser I'm using now. Comes up fine in MS Edge, so you might want to check it out. 

There is a grade of carbide insert for aluminum, and if you use it on cast iron or tool steel it might not work well, might chip badly, etc. One of the guys I was watching on youtube recently had a bunch of that stuff and was using it for everything he did, but he had to play with feeds and speeds to get it to work on the material he was using, which was mostly not aluminum. Wish I could remember who it was... Finding it might help you out. Best of luck to you, and hope this helps you.

Bill in OKC

William R. Meyers, MSgt, USAF(Ret.)

Aphorisms to live by:
Good judgement comes from experience. Experience comes from bad judgement. 
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your schedule.
The only reason I know anything is because I've done it wrong enough times to START to know better



On Thursday, July 14, 2022 at 10:02:52 AM CDT, Mike Poore <mpoore10@...> wrote:


Ideally, I'd like to be able to use one tool to take a heavy cut followed by an acceptable finishing cut. Is that possible with carbide on a 9A?

You and Ondrej recommend 400-600 sfpm with carbide. I take it carbide cuts better at a faster sfpm? Maybe I misunderstood carbide usage. I thought it was capable of faster cutting, but faster cutting was not essential for a good cut. I know the speed effects the chipbreaking, but I did not know slower cutting will actually make the finish worse. So will cutting at a lower sfpm lead to the tearing finish that I wrote about originally?

I have about 100# of various carbide inserts, so I'd really like to find something I can use rather than buying something else.

Mike

On 7/14/2022 10:10 AM, Bill in OKC too via groups.io wrote:
I'm afraid that you need a much sturdier/more massive lathe than the lighter SB lathes. My experience is with Clausing-Colchester 13 & 15 inch school lathes. The smaller 13" lathe weighs about 2700 pounds, the 15" lathes about 3800lbs. My Heavy 10L weighs just over a third of what the smaller CC lathe weighed and about has to be a great deal less stiff. Mild steel, in our class was specified 90SFPM for HSS, and 400SFPM for carbide tooling. I could get a mirror finish on the 13" lathe. I've not gotten to use my SB yet, just the Atlas. It's about a quarter the weight of the SB. Pretty much spaghetti comparatively. Unless your SB is one of the newer lathes and a 14" or larger you're going to need slower speeds and feeds, and shallower cuts to make up for the lesser stiffness. 

You could use carbide for roughing cuts, and HSS for finish cuts if you really need or want the fine finish. You can diamond hone HSS & carbide if you need it sharper, but that can mess up your repeatability with indexable inserts. 

Arwarnerco.com sells HSS indexable inserts which the folks who use 7x mini-lathes a lot seem to find very helpful. LittleMachineShop.com sells the smaller sizes appropriate for the 7" and similar machines, and in smaller quantities IIRC.

HTH!

Bill in OKC 

William R. Meyers, MSgt, USAF(Ret.)

Aphorisms to live by:
Good judgement comes from experience. Experience comes from bad judgement. 
SEMPER GUMBY!
Improvise, Adapt, and Overcome.
Physics doesn't care about your schedule.
The only reason I know anything is because I've done it wrong enough times to START to know better



On Wednesday, July 13, 2022 at 09:46:54 PM CDT, Mike Poore <mpoore10@...> wrote:


I am sure this is not the first time for this topic, but I'd like to know what setup, if any, anyone has found that provides a good surface finish using carbide on 1018?

I have acquired a lot of carbide inserts and holders along with my QCTP. I have negative rake and no rake holders. I have chipbreakers and flat carbide. I turned some aluminum after rebuilding the lathe and the surface finish was as good as one could expect so far as it was nearly a mirror finish using the slowest feed. Then I tried 1018 with the same tooling and ended up with a fairly rough finish. It looked and felt like the metal was tearing rather than cutting. I have tried other combos and nothing yet is satisfactory. I have a diamond disc sharpener, but I think the carbide is sharp enough to do better than it is. There is plenty of HSS laying around that could be used, but the idea of indexable carbide would be preferred if I can make it work.

There is plenty of experimenting left to do. I was hoping someone could give me a starting point as far as insert shape, rake, speeds (I am guessing it might be a little different than what the book says for an old WWII cast iron bearing lathe.), and tool angle. Thanks for any help.

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