Parting

[Ray C]

I hear what you're saying. For your setup it doesn't work. I leave my compound at 30 degrees but when I use the parting tool for a quick shoulder groove, I just loosen the QCTP and rotate it to be perpendicular. Quick & dirty. All the threads I do are typically just an inch long but they're oddball because it's usually 18 TPI with a shaft diameter anywhere from 0.75" to 1.25"... Sometimes it's metric though and usually 1.25 mm/Thread.


And yes man, I get my share of thread repairs on those shafts. They come in banged-up and I need to line-up threading tool carefully as there are no dies that I know of (or can afford) with those oddball sizes..

Ray; One of the main things we do is threading, so much we had to work all day Sat & Sun. for Monday. And I hate production work or my back hates it.
The job is 5/8 bronze with double end 11tpi. in range of 12" to 28" long. My first thoughts are; 4jaw chuck is out, 3 jaw is junk, has to be done on
centers. So the GK 1918 will center drill one end & campher, flip it do the same thing, thats all that lathe will do. Now it goes to my Model A I love it.
to thread between centers. Back to the post. correct or not I dont care, as my compound is set to 29.5 I stick the parting
tool in it, and do a releif cut for the depth I have to go or close, it doesnt care! Im thinking if this is to be steady work, I think I'll have to break down,
for a quick change for the GK thats big bucks then my son can do the centers champhers and releif cuts. one less thing I have to do.
I hate to be long winded or whine, kick in the buck, Sat. after 75% done customer comes in and now wants one side threaded to 3 Inches. If anyone
knows whats involved with adding on to a perfect thread with a releif cut?? just ask my back; there went Sundays lawn mowing. And then I had a
brain fart! Have a new one of those saw blade craftsman clocks Chrismas present, new, stuck it behind lathe. zero it, and I got it down to nine
min. dead start to finish (for one side) cheap time clock. hey good idea a real time clock conclusion; for this, no need to be perpendicular parting
a releif cut for threading.

 

[SE18]

I don't have a bandsaw, so I have to part off fairly often. On the occasions when I do have trouble, it was because on a deep cut I didn't take the time to make sure the parting tool was absolutely 90 degrees to the piece being cut and the extra side drag towards the end of the cut breaks the tool. I used to have an old Logan that would not part steel no matter what I did. I finally cured the problem by eliminating the compound slide altogether and made a tool post that mounted directly to the cross slide. A fringe benefit was that nearly all lathe operations improved with the added rigidity. The exception was threading. Without the compound my threads were always kinda grubby looking but they worked OK.

I don't have a bandsaw either and I use parting, usually but not always without too much problem. I'm very curious about how you eliminated the compound slide and made tool post mounted directly on the cross slide. This seems to make a lot of sense as one less thing to vibrate or wiggle. Perhaps you have a link to your work. I don't want to hijack this thread but it really is related and sounds like a good setup

 

[samthedog]

I've done a lot of parting in my life as a machinist and the key is, as others have said, having a rigid setup and the parting tool on center. Other keys to success are the correct speed, some tend to part off too slow, use plenty of cutting oil, and the parting tool must be absolutely parallel with the cross slide travel. Even a slight misalignment of the parting tool will cause problems, i.e. one side of the parting tool will drag. This creates side force that results in poor surface finish, parts that are not flat, and broken parting tools. Care in your setup will result in quality parts. How do I know this? Just yesterday I made a .015" thick thrust washer that was about 1-1/2" OD by 1/2" ID. The surface finish on the parting tool side was as smooth as the side I faced with a turning tool and the thickness was uniform across the 1/2" cross section.

Hope this helps.

Tom S

All these points are absolutely critical, especially the cutting oil. Many people do careful setup, get the parting tool perpendicular to the piece, but because they fail to use cutting oil or coolant they end up getting poor results. I have found that parting tools are more prone to chip welding when not using cutting oil as you take a shallower cut, and this eventually causes issues. Also given the ease of sharpening HSS parting tools, I don't understand why so many people insist on using them blunt. A sharp parting tool (or just a quick hone) with cutting oil makes a world of difference.

Paul.

 

[FarFar]

I don't have a bandsaw either and I use parting, usually but not always without too much problem. I'm very curious about how you eliminated the compound slide and made tool post mounted directly on the cross slide. This seems to make a lot of sense as one less thing to vibrate or wiggle. Perhaps you have a link to your work. I don't want to hijack this thread but it really is related and sounds like a good setup

My parting system is expensive but Foolprof

http://www.homemodelenginemachinist...arbide-partoff-tooling-long-10176/index2.html

Kind regards

 

[Dan_S]

I have a little 8x12/14 and even on that I have no problems parting. The key is to minimize tool stick out and rpm, and use a lot of cutting fluid. you also want to use the narrowest T shaped blades you can.

 

[awander]

While I never had the problems with parting that seem to plague some, it was still never as easy and foolproof as i would have liked.

I was using an AXA-type QCTP, on top of a stubby platform that I made to replace my compound slide(I have CNC so do not need the compound slide).

Every so often, if I fed too fast, the work would try to climb the tool, and i blamed this on the severe positive rake of the parting blades in the AXA holder. I did by some nice USA-made cobalt steel blades, which seemed to work a lot better, but still gave me occasional problems.

I was reading, 9 or 10 months back on another BBS, about a member who had gone to the Iscar-type inserted carbide parting tool, and liked it a lot. I put it on the back burner because of a lack of funds, but a month or so ago, I came upon an ebay auction which netted me (30) Korloy inserts for $2 each, in the GTN-4 size.

I was able to find a holder/blade for these inserts for about $30(also on ebay), in the 1"/26mm height.


Then I went looking for a holder for my AXA toolpost. I was surprised to find that as far as industry-standard dovetail holders to fit my AXA toolpost,this style is only available for 3/4" high and 1.25" high blades. Nothing for the 1" high blade.

After hours of searching on teh internet, i found that it seems my only option was to buy a blade holder block with a 1/2" high clamping piece on the side, which would allow it to be held in a standard turning/facing toolholder on my AXA. I found these at shars.com(part number 404-0459) for about $30 each.


So now I was about $90 in to this.

I finally tried it out the other day, and it works so much better than the flat-topped, angled 3/4" high blades, that I was actually surprised. Parting was now like cutting butter.

I only did a quick test on a piece of 1" round tool steel, but it worked like a champ! I wish I had bought this years ago.

 

[epanzella]

I don't have a bandsaw either and I use parting, usually but not always without too much problem. I'm very curious about how you eliminated the compound slide and made tool post mounted directly on the cross slide. This seems to make a lot of sense as one less thing to vibrate or wiggle. Perhaps you have a link to your work. I don't want to hijack this thread but it really is related and sounds like a good setup

Unfortunately it was years ago and I no longer have that lathe or pictures of the toolpost, but I can describe it as it was pretty simple. It was my first lathe so I signed up for a night machining course at a local tech school. They had a bunch of Bridgeports and lathes. Once I felt comfortable running my lathe I realized it's shortcomings compared to the night school machines. The final exam was to build anything we wanted (you couldn't fail the course if you wanted to) so I decided to build a toolpost to go in place of the compound. My compound was held on by a center thru-bolt that had a tapered circular piece on the bottom that went into a receptacle and was secured by a pin pushed in by a capscrew on the side of the x-slide. I found a 4 inch cube of steel in the scrap bin so I cut a slot 1.5 inches tall and 3/4 deep on one side. I tapped the top for long setscrews to hold the old style tooling from my lantern post. On the other side a cut a slot for a cutoff tool and milled a retainer that tightened down on it. The center of the block was drilled thru to use the original bolt that held the compound. The final piece started as a one inch thick slab of steel that was 4 inches wide and 6 inches long. I milled a long slot down the center and then milled the one inch thickness on a taper so I had a 4x6 inch piece that was 1 inch thick on one end and tapered to 3/4 inch thick on the other end. This piece was to go between the tool block and the cross slide so as to be able to slide back and forth for a fine height adjustment. The course adjustment was done by just piling up lathe tools and what not. With the fat end of the plate towards the work it added positive rake and when turned 180 degrees it produced some negative rake. Simple and crude but the added rigidity really improved that worn out old Logan.

 

[GK1918]

I have a little 8x12/14 and even on that I have no problems parting. The key is to minimize tool stick out and rpm, and use a lot of cutting fluid. you also want to use the narrowest T shaped blades you can.

True, all I can say being a seat of the pants flyer, listen to the machine and feel it, they do speak, and once you understand their language you will have it made, trust me. And when I said "understand their language" it doesnt mean to jump on another machine, then you have to understand >that machines language" . My two South Bend twinnies, one speaks to me, the other I swear is female. You all can relate to that example.

 

[SE18]

thanks, espanzella, appreciate you taking the time to explain

 

[samthedog]

True, all I can say being a seat of the pants flyer, listen to the machine and feel it, they do speak, and once you understand their language you will have it made, trust me. And when I said "understand their language" it doesnt mean to jump on another machine, then you have to understand >that machines language" . My two South Bend twinnies, one speaks to me, the other I swear is female. You all can relate to that example.

I think you have hit on a critical point. If your not in tune with the machine you can make all manner of mistakes. The lower the HP and less rigid, the more you need to pay attention. There is a world of difference between my old Emco Maximat V10 - 160 kg and 1/2 HP, and my Colchester Chipmaster - 550 kg and 3 HP.

Also, depending on the metal being cut you really want to avoid rubbing that results in work hardening. Getting the consistent cross feed and metal to peel off in ribbons comes with time. It just comes down to sticking with it and not avoiding parting because of a bad experience. My routine is:

1. Check the tool is sharp
2. Check tool height
3. Check how far out it protrudes from the tool holder
4. Check that it is perpendicular
5. Check lathe speed
6. Check cutting oil and brush are close by
7. Make sure the part is not sticking to far out of the chuck to avoid flex and chatter
8. Check cross slide to avoid excess hang-over
9. CUT!

This seems like a lot of steps but these usually take a glance and are fairly ingrained. Again, I can't stress the importance of a sharp tool and cutting oil enough!

Paul.