Parting Problems – Backlash ?

[Dan CarterParticipant @dancarter89683]

Jason,

Photo of motor mounting below – the cold may have finished me off but I don't see much useful adjustment.

Muzzer – I wish. Actual ranges are 30-450 and 150-2500. I don;t use 2500 much

Vic – I tried one of the blades jury rigged in my dickson parting holder, but am planning to buy a real holder. It seemed to work pretty well before my latest round of woe.

John – Yes, at some point I reckon a new pully will be on my long to do list.

[Chris Evans 6Participant @chrisevans6]

Looking at that picture you could make up a jockey wheel to tension the belt. Plenty of room to tap some holes in the end of the bed. I wish my lathe would go down to 50 RPM I find 80 to quick for some screw cutting.

[John McNamaraParticipant @johnmcnamara74883]

Power Feed?

Sure if you are doing a batch and can test: for one offs I prefer to hand feed, this enables me to pull back if the sound changes to the growl that often accompanies a dig in.

Regards
John

[AjohnwParticipant @ajohnw51620]

Must admit I never power feed when I am parting off or facing – I'm usually using a boxford with a gearbox so setting the rate is easy and quick.

It's a bit strange that they haven't allowed for belt tensioning. Maybe there is some scope in the motor mounting. They shouldn't need to be that tight with sensible pulley sizes as they tend to pull in and grip on the side that is transmitting the power.

John

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[Nick_GParticipant @nick_g]

Posted by Ajohnw on 20/01/2016 23:56:07:

It's a bit strange that they haven't allowed for belt tensioning.

John

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I agree. Very strange if that proves to be the case.

However. This product **LINK** will probably get you out of a tricky spot as you can make it within reason virtually any length you wish. It's OK if it's a tad tight to start with as it beds into the pulley grove with a little use. – Make sure you get the right width though.

Lots of people on this site use belts such as this. Myself included.

Nick

[JasonBModerator @jasonb]

Quite a different mounting method to that used on the 280 which has a flange mounted motor

[egaParticipant @ega]

John McNamara:

Those who choose to hand feed are likely to find an extended cross slide handle helpful – see the DHC photo I posted earlier in this thread.

[AjohnwParticipant @ajohnw51620]

If you do go for a linked belt I would avoid buying the cheap black one. (RDG I think) In use it's a bit like trying to use toffee.

The T and nut types that use metal link joiners are fine but not the easiest thing to join up. Fenner make one that doesn't use metal joiners but have chosen to only sell it in rather long expensive lengths. Maybe that one is ok.

Not sure what section your belt is but if you look here for instance at A section the steps in size get smaller as the belt length goes up. This is the way I would probably go, Cheaper and efficient – even if you have to buy 2.

**LINK**

John

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Edited By Ajohnw on 21/01/2016 09:39:05

[Ian S CParticipant @iansc]

I had a Fenner Power Twist belt on the primary drive of my lathe for nearly twenty years, I replaced it a couple of months ago with a similar, but non Fenner belt, it's taking it's time in settling in, does not have the feel of the old belt, but is getting better.

Ian S C

[Dan CarterParticipant @dancarter89683]

it is a bit of slack fit, and I doubt it helps that the motor pulley for low range is small – about 4 or 5cm diameter without measuring. As suggested above, a tensioner would be easy enough – in fact it could fit on the stud to hold the cover on without any further drilling required.

I think I will try a slightly shorter belt for now, but then the Chronos link belt in Nick's post will come in handy as on reflection I will be trying to change the pulleys sooner rather than later – I don't much want to have to change belts between turning and parting operations …

Thanks to all for bearing with me – would still have been flailing about feeling grumpy otherwise.

Regards,

Dan

[Ian S CParticipant @iansc]

An idea that I used on my vertical mill. Because the small pulley on the motor, some where about 40 / 50 mm, this is far too small for a B section belt, I went to the local Garage and got a suitable size fan belt that has notches in the inside of the belt allowing it to fit on a smaller pulley, it's done alright for the 25 years, looks as though it will last 25 more.

Ian S C

[Dan CarterParticipant @dancarter89683]

Grrr. Just in case anyone ever has the same problem and is as daft as i am, the tension can be adjusted.

The axle for the middle pulley (top one in picture above) is mounted in a vertical slot with a t-nut behind, so it can be shoved up a bit. The slot was covered by a washer and I hadn't noticed it until I started looking at which pulleys would be easiest to change to alter the speed range.

[Bruno TaylorParticipant @brunotaylor21701]

I initially had problems parting off with my WM250. All the symtons mentioned above.

I then sought instruction and found Tubalcains videos on YouTube. I followed his advice and now part off with spectacular success.

I use carbide inserts just below centre.

Key points, not too fast, about 1/3rd normal macining speed. Lock the saddle and power crossfeed as slow as possible using selectors ( not gear changes or low range ). Minimum overhang, both tool and topslide. Lubricate harder/tougher metals.

Incidently l also used Tubalcains advice to cut my first course (16TPI) thread in stainless steel.

[Nicholas LeeParticipant @nicholaslee]

This might only be a contributing factor to the problem, but the "surface feet per minute" (SFM) cutting speed of your parting operation will vary with the ever decreasing radius, as the cutting tool moves in towards the centre of the bar.

What is a sensible calculated cutting speed for your material at the outside of the bar may be completely wrong by the time you get near the middle of the bar.
If the SFM for the tool and material goes too low then it will start creating the wrong shape chips and it could clog the slot, overheat the tool, or start rubbing rather than cutting. If this causes metal to start adhering to the tip of the cutter, then as it is in a narrow slot it can cause it to jam and snap.

Modern CNC machines are smart enough to continuously adjust the spindle speed during a parting operation to keep the SFM a constant.

On a manual lathe you might want to consider emulating this by pausing the parting cut half-way through, withdraw the tool, then increasing the RPM to finish the parting-off operation.

The other side of this coin is feed rate. This also affects proper chip production.
Check the shape and colour of the chips, and see how they change as you do your cut.
That should tell you what's going on.

[JasonBModerator @jasonb]

No need to stop and change speeds on a 290, just wind up the wick on the variable speed as you get nearer the centre

Edited By JasonB on 29/01/2016 16:24:03

[Ian S CParticipant @iansc]

I'v seen the same done on a Chipmaster, as the tool went in, the operator just turned the speed control wheel, 4" bar in no time flat.

Ian S C

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