Best Method for Parting Off

Rick_B · Oct 18, 2014

Good evening folks - here's the scenario, I'm starting with a 3" diameter piece of material in a 4 Jaw chuck. Then I'm offsetting the center of the material by a 1/4" in the X direction. Then I will be drilling a 3/4" hole followed by boring that to 2" diameter. This work will be done on a wide bed SB 9" with a large spindle.

So now the question - I need to part off a 7/16" piece of the drilled and bored material. I think there may be at least two methods
1. leave everything off set in the 4 jaw and part off. This will result in interrupted cuts on the external surface for a large part of the cut.
2. Put the 3" diameter back on center and part off - interrupted cuts internally for a large part of the operation.

It seems that option 1 may be the best way but I thought some expert input was called for. Any thoughts or other potential methods?

Thanks
Rick

mach2 · Oct 18, 2014

Make the cut off disk first then bore the holes. Parting 3" in a 9" lathe in my opinion is crazy talk.

1. Saw off the disk.You will need about an inch
2. Face one end and turn to diameter at least 1/2".
3. Turn over using the newly turned diameter and face to seat the work. face other side so part 7/16" thick.
4. Bore the holes.

No parting involved then.

Tony Quiring · Oct 18, 2014

That little lathe not good for parting that.

Cut to length plus margin with band saw first.

Face both ends to size.

Shift then use face to verify still square.

Proceed to drill and bore.

I would not part off this part with my 16 L&S...easier to let the band saw do it.

Rick_B · Oct 19, 2014

Guys - I understand what you are saying about parting off with a 9" lathe but I was thinking that after the offset 2" hole is bored I would be parting through a max of 3/4". Here's a picture of a template I made of the final piece. This is only 1/4" thick(versus 7/16) but it shows what I am talking about

Does this perhaps change your opinions about parting off?

Thanks
Rick

kitno455 · Oct 19, 2014

Do not recenter the stock's OD before parting. Interrupted OD cut is fine. Interrupted ID cut sucks- you will find that the piece of stock begins to flap back and forth on the remainder of the thick side, and then it does something crazy like dig in. I would expect to have to take a facing cut on the parted side of the work piece, so leave enough stock for that, or just use a bandsaw.

allan

Rick_B · Oct 19, 2014

Thanks Allan - band saw would be my preference. Unfortunately this piece is needed to get my power hack saw working and my metal cutting band saw is in pieces in the rat hole

Rick

specfab · Oct 19, 2014

If you are stuck with doing it via parting off, then yes, the ID should be centered. Good luck with that cut on that small lathe. I suspect slow speed will be your friend (assuming this is steel). If I were doing that, I likely would have started with something I could just face to thickness at the outset. (Easy for me to say.)

Tony Quiring · Oct 19, 2014

Try this...

Recenter for full cut on od.

Start to part off long enough for some error.

After you have good groove all the way arround get out hacksaw or recip saw and cut manual with grove as guide.

Flip after cut and clean up with facing cut.

It is a one off...

moonlight machine · Oct 19, 2014

Steel? Aluminum? Your lathe is a flexy flyer, probably chatter like hell on steel. Don't think so hard about it, it is just not a big deal. Steel.....back gear, slowest power x feed lube it and giver hell. Aluminum....higher spindle speed. Leave the hole centered. Just do it.

Zonko · Oct 19, 2014

Tony Quiring said:
I would not part off this part with my 16 L&S...easier to let the band saw do it.

That is not true.....
Parting off 3" is a piece of cake with a proper 1/8" insert tool and a 16" lathe....

conant · Oct 19, 2014

If only making one proceed as you started and bore off set. BEFORE you part off get a tool back ther behind the excess length to get rid of most of the material. Do a back face up to the diameter that is left. Now simply part off the remaining section that is running true.

Sounds like a one part repair and that is how I would do it.

Rick_B · Oct 19, 2014

Just some additional info - yes it is steel piece and it is a one time event for a repair

Thanks
Rick

garyphansen · Oct 19, 2014

I have a Model A 9" and that is well within it's capabilities, if the lathe is in good shape and you know what you are doing. I would use your option number one, but I would turn down an area perhaps an inch wide with a normal lathe bit until you were cutting all the way around the part. Then I would part it off. Here are some tips. Use cutting oil if you have it, the dark smelly sulfur kind. At least use some car oil if you don't have the right kind. Drip to oil into the cut as you cut it. Use a live pipe center in the tail stock. I hope you have an Aloris or Phase II style tool post because they have more rigidity and so work better than the old lantern style. American made Empire HSS parting bit will work much better than China made HSS. In any case you need to sharpen it because they don't come from the factory sharp enough. After you sharpen it put a nick in the center, that will cause the chip to fold in the center so it doesn't get caught between the tool bit and the side of the cut. Gary P. Hansen

garyphansen · Oct 19, 2014

Let me add that most people try to part to slow and with the correct feed and speed it works better to part with power feed instead of turning the crank by hand. Gary P. Hansen

Oldwrench · Oct 19, 2014

Poor planning. If your tool digs in it will cause much wailing and gnashing of teeth. And possibly rending of garments. On a tiny machine like that, the work would be much easier if you faced the part 7/16 thick FIRST. Then you're not doing any interrupted cuts, just offsetting it to bore the hole.

traditional-tools · Oct 19, 2014

Rick_B said:
Thanks Allan - band saw would be my preference. Unfortunately this piece is needed to get my power hack saw working and my metal cutting band saw is in pieces in the rat hole

That's a 5-10 minute cut with a hack saw, taking your time to stay close to your line (yes, I recommend marking it).

Clean the end up on your lathe after.

Cheers,
Alan (another one with a different spelling

)

conant · Oct 19, 2014

whatever you do take your time and think it out carefully. Lotsa cutting oil!

rwbaldwin · Oct 20, 2014

Zonko said:
That is not true.....
Parting off 3" is a piece of cake with a proper 1/8" insert tool and a 16" lathe....

With the right parting tool (1/8" or 5/64" insert), even the 7x hobby lathes can do this with ease

Hoppy · Oct 20, 2014

I'm called upon to do one-offs like this all the time. The best option is to saw off a chunk of stock and face both sides. Make your thickness about 0.03" or so more than your finished dimension. Load up your 4-jaw and bore. Do not bore all the way through and hit your chuck jaws! Stop the cut somewhere in the 0.03 extra material. Turn the part around and face off the extra material after the bore is complete.

Since you may not have sawing equipment, use a regular turning tool after you've finished your bore and remove some material until you can run your parting blade without an interrupted cut. By all means, leave the bore on center! Parting into an interrupted cut will ruin your day!!

Rick_B · Oct 22, 2014

Well folks - job completed. A little back ground - this cam like part is being used to replace a very worn cam surface ob the baxk of the driven gear for a power hacksaw. I had previously machined off all of the worrn area and left enough of the profile to determine that it was simply a 3" circle with a 3" offset hole. Here is the machined gear

Then I made the template above just to verify what I thought the profile was. This morning I used a 3" dia by 3" thick piece of round stock, chucked it up and faced both ends, offset the piece by 1/4" in the chick. Then I drilled a 3/4" hole (using a variety of smaller bits to step up to 3/4") followed by boring it out to the 2" size. Then I took a deep breath and started parting it off so it was a little over 7/16" thick. That was a bit scary with the offset piece flopping around and the interrupted cuts but I kept on going. I was going to stop and finish it with a hacksaw but before I made up my mind I was through it.

Finshed puece

Ring fitted to gear

Once I was happy with the fit I drilled and tapped some holes in the gear and used clearance holes in the ring to fasten it in place.

Thanks for the advice and help with this little project

Rick

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