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Tooling Selection

RV-N8ZG

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#1
Gentlemen -
I have an OXO-size QCTP from LMS mounted on my Jet 9x20.
Since the tool holders are big enough to accept 1/2" stock, I bought a SHARS 1/2" indexable insert set, rationalizing that even if the lathe can't take advantage of the additional rigidity over 3/8" stock, it can't hurt. I know, silly newbie mistake.

Problem: Unmodified, the stack-up is too tall for the 1/2" tools by something less than 0.125" (haven't measured). I don't have ready access to a mill to shave the top of the compound or to shave the bottoms of the holders. I can probably encourage a better-equipped friend to do a little mill-based adjustment if needed. I have filed a relief on the corner of the compound that allows the tool holders to drop low enough to get the correct cutting height for the few tools that I have.

Two questions come to mind:
1. Given the natural "strength" of the 9x20-size machines, is there any advantage to be gained with 1/2" vs. 3/8" tool holders?

2. The first order of business is a Pitkin Donut. Would you consider it wise to either make the donut thinner or shave the top of the compound to allow the QCTP to accept 1/2" tooling?

Neal
 

mikey

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#3
Neal, that size lathe would be fine with 3/8" tooling. My friend owns an Emco Compact 8, which is what the 9X20's are cloned from and it, too, cannot get a 1/2" tool on center. Even my Emco Super 11 cannot get a 1/2" tool on center without modding something.

I use mostly HSS 3/8" tooling on my lathe and I can cut anything I need to with those tools. I also have 3/8" inserted carbide tools and have no issues cutting any material in my shop. While it is true that a larger tool is more rigid, your lathe is not rigid enough to take advantage of a 1/2" tool so I would avoid them if I were you.
 

darkzero

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#4
I agree, I wouldn't even worry about 1/2" tools especially if you grind your own HSS tool bits. You won't notice a difference with 1/2" tools with your lathe unless you stick them out pretty far.

I had an AXA on my old 8x14 lathe. The bottom of the tool holders had to milled for 1/2" tools to reach center height. I didn't have a mill at the time. 3 ways or getting around it. Either mill the tool bits, the tool holders or the compound slide (if able to). I didn't want to mill the compound slide but that would have been the best way.

What I did was bought a bunch of tool holders & took them to a local engine machine shop that I used when I worked in automotive. They charged me very little & even chamferred all the edges to match the other chamfers. Take them to a regular machine & they'll most likely charge you way too much.

That way any 1/2" tools I bought in the future I could just pop them in without modification. If you mill the compound slidex then you wouldn't even have to mill any new tool holders.

The only advantage with 1/2" tools over 3/8" in this case is if you are looking to use indexable tools. Much more tooling available for 1/2" than in 3/8".
 

savarin

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#5

RV-N8ZG

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#6
Thanks folks - that's about what I expected.

Charles -
I intend to make a plinth as well.
I'm in a bit of a chicken/egg pickle as far as where to start, what to do first. I have a 3" 3-jaw , but no external jaws for it, so I can't mount the blank directly in it. Also have a 4" 3-jaw, but the backplate adapter is not fitted.

I'm a mite confused over how to begin fitting the adapter. Mounted normally, it is a little out of plane; but mounted backwards, so as to face the spindle registration boss, the run-out is much greater. Haven't measured it yet, maybe I'll get to it this weekend. The chuck-side of the adapter has a chamfer at the spindle hole - do I trust that the threads and chamfer are true, stop fretting and just cut it?
 

Silverbullet

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#7
Since you own the insert tools why not get the bottoms of those milled down the .125 you need?
 

savarin

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#8
I'm a mite confused over how to begin fitting the adapter. Mounted normally, it is a little out of plane; but mounted backwards, so as to face the spindle registration boss, the run-out is much greater. Haven't measured it yet, maybe I'll get to it this weekend. The chuck-side of the adapter has a chamfer at the spindle hole - do I trust that the threads and chamfer are true, stop fretting and just cut it?
I'm unsure what you mean here, is it the new back plate when screwed onto the lathe spindle does not run true?
Does it screw right up to the flat end of the spindle?
If its the first one can you not just take a facing cut to true the face (both sides?) and a skim from the dia.?
Could you mount what you have to a face plate t sort it out.
I'm not a pro but heres how I made my back plate for the 4 jaw, also a bunch of my questions answered that may be of help.
http://www.hobby-machinist.com/threads/9x20-chuck-backplate.29698/
http://www.hobby-machinist.com/threads/aligning-the-holes-in-the-back-of-a-chuck.30732/
You will note I'm still using the compound it was so long ago when I was beginning.
 

RV-N8ZG

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#9
I've been away from the tools for a couple weeks, so my recollection is a little fuzzy.
I'll get some photos and measurements this weekend...
 

RV-N8ZG

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#10
I was able to get back to the hangar and tinker with the lathe this weekend. I re-mounted the adapter and the run-out was not nearly as bad as I thought. I also called LMS ask about close to true I should expect the registration boss and threads to be as-delivered. LMS suggested I just mount it and cut it, see what happens. After chewing up both ends of a carbide insert, I tried grinding a blank labeled "Bonded Carbide" and mounted it up. Might as well have been trying to cut the grinding wheel. The cast adapter chewed all resemblance to a cutting edge off the tool in just a few revolutions. Back to the grab-bag of blanks a friend gave me many years ago, I found two that looked different that the rest. Another hour at the grinder and I had something to try. Shocked and amazed - it cut, and kept cutting. After several hours and a few re-sharpen sessions, I was able to cut the very oversized adapter blank down to fit my 5" 3-jaw and get it mounted well enough to cut some steel. Also learned that cast makes a MESS.

I spent most of today making a Pitkin Donut. Also learned that cheap carbide inserts are not a good deal, but the HSS did a pretty good job, even with my poor sharpening skills.

Thanks for the patience and input.
For future reference, it's OK to tell me to shut up and cut it...

neal
IMG_6766.JPG
 

mikey

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#11
Came out good!

A suggestion: for turning cast iron, a sharp brazed carbide bit run at low speed works well for rough facing and a good HSS facing tool will provide a very nice finish. Used this way, these tools will last a long time on cast iron. The trick, if there is one, is to go slooow with cast iron. No lube, and cover everything you can with sheeting and old towels (to catch the grit). When you're done, remove your covers and clean everything ... twice.