Ideas For Selecting Indexable Tooling

[PGB1]

Hello All!
I am very much the amateur who is on a never ending mission to learn machine shop practices. To be honest, this process has been going on for more than a decade. (I'm a slow learner.) Now, I'm old enough to have more time to use my lathe, I can practice what I read. My lathe is a South Bend 13" from 1922 that i restored over the period of a year or more.

My recent brain storm was to perhaps buy indexable tool holders to let me take advantage of the BXA quick change tool post I have. I like to grind and use HSS tools, but sometimes I would like to be able to swap tooling without adjusting bit tip height. (I can't seem to grind tool bits to have the same height.)

The BXA's holders will take up to 5/8" tall tool shanks and will hold down to 3/8" shanks. Half inch x half inch is a perfect fit width wise. The holders are labeled "250-201" and "250-202".

As background, I mostly am using mild steel, sometimes with mill slag on it. Lots of jobs are brass. I also occasionally use stainless in one of the 300 series or even junk steel once in a while. (Lots of grounding rods have passed through my lathe- Inexpensive round stock.) If I'm lucky- 12L14 is the material.

I've read that triangle inserts are the way to go and I have also read that diamond is best shape. I surely do not know what the advantages are for either over the other.
I noticed that 3/8 inserts are less expensive than 1/2" and I am guessing they will fit into tight places easier than 1/2 but have less support at the tip.

Am I on the right track thinking about 3/8 shanks- Or, perhaps, abandon the idea all together since I don't do any production work and put the money in my "Sweetheart, we really need a milling machine" fund?

Thanks for sharing any thoughts you all have!
Paul

 

[Rbeckett]

I prefer the 1/2 square tool holders with a 3/8th IC triangle bit like a TCMT or similar. those bits are kind of pricey, but if used properly and rotated correctly you do get quite a bit of use before they dull. interrupted cutting will end a carbide insert quickly, so I round off the job first with HSS then change to carbide for the finer points. This really stretches the carbides usefulness and gets the longest life possible from each surface. I keep a huge handful of HSS bits sharp and ready to install in my QCTP holders and adjusting them to center is not difficult or time consuming once you have it close already. I would definitely start a mad money pool to get a mill if I didn't already have one on it's way. Look around in your area for auctions and foreclosures because a lot of shops are going bust with the poor economy and the machines are readily available for much less than new and already industrial rated so you can get some serious work out of them to help repay your investment. You might also look around at some of the local shops and see if they need some small runs of brackets and trinkets that you can easily produce on your lathe and mill once it arrives. Just keep in mind the machine is the cheap part. Tooling and accessories will be where you invest the most of your hobby money. In that case, Ebay and the local flea market can be your very best friend. I often find mis spelled tooling and improperly classified tooling for cheap because the seller doesn't even know what they are or care enough to spell it correctly in the description.. So they often relist it for much less than it is actually worth to just get rid of it... Hope this helps..

Bob

 

[PGB1]

Thank You, Bob, for your thoughtful and helpful reply.
I had no idea that interrupting a cut would damage the carbide. Wonder why that happens?

Is the damage from interrupting & re-starting without backing the bit off first or is it harmful even if the tool is backed off and re-enters just as if it was the next pass?

I have broken pieces of the tips off a couple of inexpensive tool bits that come with the carbide tips already cemented to the steel blank. I must have weakened them when I stopped & re-started a cut.

Your tip about using HSS first is going to be my practice. I'd rather destroy something I can repair easily than wreck a piece of carbide.

Thanks, too, for the ideas about putting a milling machine to work to help pay for itself. I have referred some jobs to others which I could have done with a mill. Most were either bus bar customizations for bus plug adaptations or instrument panels for electrical equipment. Good jobs for an amateur.

In the Detroit area there are still many small shops being sold off. The economy is improving around here, but I think only the larger of the auto suppliers are getting busier so far. Hopefully, soon there will be so many shops re-opening there will be no equipment to buy!

Thanks Again for your great article.
Enjoy Today!
Paul

 

[TomS]

I have an AXA tool post on my 12 x 36 lathe (bought originally for my 9 x 20). I have 1/2 square indexable tool holders that use TNMG inserts. These inserts have 6 cutting tips and are inexpensive. I watch for sales and usually buy them in lots of ten for less than $3.00 each. The downside to these inserts, if you want to call it a downside, is that they are negative rake. They require more HP when making heavy cuts and getting a good surface finish can be challenging on certain materials. Having both negative and positive rake holders and inserts would be ideal if your budget will allow it. And I agree with Bob, interrupted cuts with carbide will chip the cutting edge unless you are taking light cuts.

Hope this is helpful information.

Tom S.

 

[LEEQ]

The interrupted cuts being referred to are things like turning square stock round. Anything else that would have a brief space not contacting the tooling would be similar. A shaft with a keyway in the section you are turning would also qualify. I might add that I did a lot of reading to figure out which bits for what material when shopping for inserts. Makes my head hurt. Good luck.

 

[PGB1]

Thanks LEEQ & TomS for sharing great thoughts on the subject.

Maybe, since I am still learning, using TNMG will be a good plan. Having the extra 3 tips certainly should come in handy as I learn and practice. I never thought about getting negative and positive rake holders instead of negative & positive inserts with neutral holders. Your idea will certainly be a money saver.

It has been quite interesting studying the different types of holders and cutting inserts. The tip & holder designation nomenclature are (almost) starting to be recognizable when I browse catalogs.

Thanks LEEQ for the details about interrupted cuts. I have broken tips while making what I thought were light cuts on a shaft with a keyway. I probably was not light enough.

When they get damaged, those bits with the cemented tips then get the tips sawed off and the shanks become shim stock or go in the shaft key drawer. The tips go in the scrap carbide jar. If the tip's broken spot was small enough, once in a while I could save a tool by re-grinding with a diamond wheel I took out of a scrapped Drill Doctor machine. Not the finest grind job, but OK for practicing I guess.

Thanks Again for these lessons.
My Wife and I Would Like To Wish Everyone Who Reads This A Very Happy and Peaceful New Year!
Paul

 

[Bill C.]

Thank You, Bob, for your thoughtful and helpful reply.
I had no idea that interrupting a cut would damage the carbide. Wonder why that happens?

Is the damage from interrupting & re-starting without backing the bit off first or is it harmful even if the tool is backed off and re-enters just as if it was the next pass?

I have broken pieces of the tips off a couple of inexpensive tool bits that come with the carbide tips already cemented to the steel blank. I must have weakened them when I stopped & re-started a cut.

Your tip about using HSS first is going to be my practice. I'd rather destroy something I can repair easily than wreck a piece of carbide.

Thanks, too, for the ideas about putting a milling machine to work to help pay for itself. I have referred some jobs to others which I could have done with a mill. Most were either bus bar customizations for bus plug adaptations or instrument panels for electrical equipment. Good jobs for an amateur.

In the Detroit area there are still many small shops being sold off. The economy is improving around here, but I think only the larger of the auto suppliers are getting busier so far. Hopefully, soon there will be so many shops re-opening there will be no equipment to buy!

Thanks Again for your great article.
Enjoy Today!
Paul

Sadly I broke a lot of cemented carbide tool bits on my first job. They had me run a (I think 36") Bullard vertical lathe. I remember turning large forgings so another machinist could mount them on a horizontal lathe with a hydro-powered tracer attachment. He turned my blanks into forging dies. My job was to remove the scale and turn them down to a working diameter. I ran short run production and other odd jobs for that shop. It was a good job for a 18 year old.