Thread: problems with cutting off

Originally Posted by morrisman

On my Sheraton 9" lathe . My thread cutting problem is nothing in comparison to my cutting off. I have a Armstrong style cut off tool . No matter what you do, it's always given trouble . The work piece eventually comes out of the chuck.... it's that bad . Seems to be a design thing , as the tool digs in and chatters . Probably too much overhang with that design . The lantern tool post seems to flex whe the cut off tool is fed into the work piece.
Is there a better way ? I do have a few cut off blades , maybe I should make a dedicated holder for them. MIKE

hi i have a more ridged tool post than the lantern style that you can have if you
like. that is if you ever get over this way. it wont fit that parting off tool you have in it
thou. you will have to grind one up.

Attachment 179741

Hi Morrisman,

If your part is coming out of the chuck, you have a pretty serious problem....

Either there is a problem with the chuck or your parting off tool is digging in,

Here are some quick suggestions..

1. Is the chuck in good condition?
2. Are you sure you have the parting tool set up parallel to the cross slide?
3. The width of the cut should be a little wider than the shaft of the tool. Maybe the tool is stuffed?
4. Is the tool set up on center, a little below won't hurt, but above center it will dig in.
5. Go to the slowest speed you can select, at least until you figure out what is happening.
6. Are you parting off as close to the chuck as you can.
7. Is the tool cutting evenly, if it's uneven, you can sometimes get twisting with the cheaper tools, and when it twists it grabs.

That's all I can think of, off the top of my head... I'm sure there are other tips.

I used to have trouble with those cheap parting tools, some of them would cut unevenly and twist.

Regards
Ray

morrisman,

I just had another look at your photo of the parting tool holder. I agree with nadroj - the spring action on your toolholder cannot be working, because the slit which should allow the end of the toolholder to move downwards to take the pressure off the blade when it is about to dig in is already completely closed at the bottom, and full of paint at the top end. If you open the slit so the sides are parallel right up to the hole near the top of the tool and clear out the paint so there is no obstruction to the movement of the end of the toolholder, you should see a definite improvement.

In the photo you have the lower end of the slit sitting on the rocker piece in the toolpost. Even if the slit was open and usable, this would prevent the end of the parting tool blade from moving downwards and away from the workpiece if it started to dig in. The bottom end of the slit needs to be clear of the toolpost, and the tool no higher than centre height, and preferably slightly below, for the tool holder to work correctly. This requires a fair bit of tool overhang, so a reasonably rigid mounting for the tool holder is an advantage. The lantern toolpost is not the best choice, though they were used successfully for many years on many different lathe types.

The blade I have on mine is 3/32" wide at the top, tapering down to about 1/16" wide at the bottom. Since I got my gooseneck tool holder I have had absolutely no problems parting steel up to about 40mm. Parting with my previous 1/8" wide tapered parting blade mounted in a rigid toolholder on the well used smaller lathe was seldom trouble free, with dig ins and broken parting blades occurring all too often. I think if you sort your tool holder out and use a tapered blade if yours has no taper, you will be surprised at the difference. A more rigid means of holding the parting tool holder would be an added bonus.

As well as fixing the toolholder, I second everything Ray says above - all these points can affect the parting cut.

Regards,

Frank.

morrisman,
I have the same tool holder as yours, but with the same 3/32'' wide tapered blade that Frank has.

This bloke sells them:
http://lprtoolmakers.auctivacommerce...-P1414860.aspx

Rgds,
Chris

Many ideas in there ..I've read it all OK . First . At TAFE they told me never to part off with the tailstock in position in the workpiece, it's disastrous and dangerous. OK I will remove the offending piece stuck in the gooseneck holder that prevents it from 'springing' .... and doing its job ! Good advice that. I do need a more rigid holder for the gooseneck . I will design a new one and hopefully that will alleviate some of the problem. I have it all set up as per the book . The chuck is OK . The cut off tool is dead on centre. I've tried various speeds , but that doesn't help . The blade in it is tapered , 1/8 wide at the top . You have all given me much food for thought . I think I will overcome this MIKE

Originally Posted by morrisman

I do need a more rigid holder for the gooseneck . I will design a new one and hopefully that will alleviate some of the problem. MIKE

Mike,

FWIW the first photo shows what I use for holding odd sized toolholders which don't fit the 4 way toolpost.

A long tee bolt, in this case the original one for the 4 way tool post, is used in the compound tee slot. A square piece of flat plate of suitable thickness (8 mm suits this lathe), goes over this bolt and sits on the compound to provide a flat surface for mounting the tool holder. A second similar sized piece of plate, in this case 10mm with a large clearance hole for the tee bolt is used to clamp the toolholder. This plate has a 10mm jacking screw on one side and a recess about 25 long by 15 deep cut in the middle of the opposite side, which leaves two short arms to clamp the shank of the toolholder, and allows the clamping plate to level itself on the tool holder. I have a couple of different length spacers for use between the clamp plate and the clamp nut to accommodate toolholders with various non-standard shank sizes.

This type of clamp is used on the Myford and a number of other small English and Australian lathes, is easy to make, and is much more rigid than a lantern toolpost. For comparison with the previous photo I have also shown the toolholder clamp on the Brackenbury and Austin lathe Maybe something similar to these would work on the Sheraton?

Frank.

Originally Posted by franco

Mike,

FWIW the first photo shows what I use for holding odd sized toolholders which don't fit the 4 way toolpost.

A long tee bolt, in this case the original one for the 4 way tool post, is used in the compound tee slot. A square piece of flat plate of suitable thickness (8 mm suits this lathe), goes over this bolt and sits on the compound to provide a flat surface for mounting the tool holder. A second similar sized piece of plate, in this case 10mm with a large clearance hole for the tee bolt is used to clamp the toolholder. This plate has a 10mm jacking screw on one side and a recess about 25 long by 15 deep cut in the middle of the opposite side, which leaves two short arms to clamp the shank of the toolholder, and allows the clamping plate to level itself on the tool holder. I have a couple of different length spacers for use between the clamp plate and the clamp nut to accommodate toolholders with various non-standard shank sizes.

This type of clamp is used on the Myford and a number of other small English and Australian lathes, is easy to make, and is much more rigid than a lantern toolpost. For comparison with the previous photo I have also shown the toolholder clamp on the Brackenbury and Austin lathe Maybe something similar to these would work on the Sheraton?

Frank.

Roger that Frank I see it's relatively simple to make up a more rigid holder like you did . I won't ditch the gooseneck just yet . Mike

". At TAFE they told me never to part off with the tail stock in position in the work piece, it's disastrous and dangerous"
I wonder why it dangerous and where Ii got the idea to do it like this. Probably i just thought the extra support would help. Im going to have a little go at parting off now..

Sometimes you have to use the tailstock.

Anorak So the workpiece in the above pic is rotating in the normal direction ? I see the tool is on the opposite side from normal ... Mike

Originally Posted by morrisman

Anorak So the workpiece in the above pic is rotating in the normal direction ? I see the tool is on the opposite side from normal ... Mike

Mike,

The parting off tool is upside down. The work rotates as normal.

Bob.

Originally Posted by Anorak Bob

Mike,

The parting off tool is upside down. The work rotates as normal.

Bob.

Roger that . Is there any physical/mechanical advantage in having the force transmitted upwards rather than downwards ? Mike

Originally Posted by Anorak Bob

Mike,

The parting off tool is upside down. The work rotates as normal.

Bob.

Details of blade holding method would be appreciated by me as well Bob.

Dean

The rear tool post excludes the compound slide as a source of movement and because the slide and cutter are in tension when parting off, the slide dovetails are pulled up tight reducing the opportunity for vibration to occur. So the story goes.

The thing works well. Having the knurling tool sharing the post is real handy. One improvement would be to have the post set up as a rotating turret thereby removing the need to rotate the entire post when changing operations. Another improvement would be to locate the lower edge of the blade in a rebate.

The pair of 1/8" socket set screws ensure the verticality of the blade.

BT