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Problem with slitting saw arrangement...

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Hillclimber06/06/2019 18:00:29
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I am trying to use a slitting saw for the first time, and on a new setup. Problem is that the saw just sticks and rotates on the mandrel as soon as I advance the workpiece into it.

The arrangement is on a Myford S7. I am using a 3"x3/32" 140T slitting saw on a 1" mandrel. The mandrel is a perfectly nice item from Arc, with a left-hand thread locking nut, which I understood was the 'right' answer to stop the nut locking itself on. I have also removed the driving key as this seems to be advisable to avoid breakages if jammed.

The workpiece is a a simple EN3 piece of round bar of about 1/2" diameter in which I am trying to cut an axial slot on the end. The bar is clamped horizontally into the slot of a Myford vertical slide and advanced by the cross slide.

The mandrel is 2MT mounted with a drawbar, and held with a revolving centre in the tailstock.

Am I correct to be using a LH locking mandrel? It certainly makes it quite difficult to do up, as that action unlocks my drawbar - so I can't counter one rotation with the other? And is it correct to remove the driving key as I have done?

Cheers, Colin

Martin Connelly06/06/2019 18:23:54
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851 forum posts
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It may help to increase the friction between the saw blade and mandrel by fitting a paper washer before putting the blade on. It will still slip if it jams but may have a little more friction than a metal to metal joint. If you have a second chuck maybe you can hold the mandrel body with it to tighten the drawbar before fitting the blade.

Martin C

JasonB06/06/2019 18:35:27
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Are there no spanner flats on the body of the arbor so that you can get it tight? I usually hold my one by the flats in the bench vice and then tighten with a long leg allen key (mine is screw type fixing) RH.

LH screw will want to undo unless you run the lathe in reverse and have the teeth cutting upwards on the operators side.

 

 

 

Edited By JasonB on 06/06/2019 18:40:08

Edited By JasonB on 06/06/2019 18:41:31

Clive Brown 106/06/2019 18:38:37
263 forum posts
7 photos

I don't think the L/H locking nut will make much difference. The 1" mandrel that I use on my small mill has a R/H thread. I would see a 3/32" saw into steel as being quite wide for a friction drive set-up.Try a washer as suggested but I'd replace the key and go carefully.

Clive

Andrew Johnston06/06/2019 18:48:42
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4849 forum posts
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How deep is the slot? A slitting saw with 140 teeth is very fine and not suited to deep slots as there's nowhere for the swarf to go.

Andrew

Peter Tucker06/06/2019 19:22:06
179 forum posts

Hi Collin,

I always use a key in a slitting saw otherwise they just slip on the mandrel.

Hope this helps.

Peter.

JohnF06/06/2019 19:39:21
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864 forum posts
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Colin, no reason why you should have a LH thread as long as you make sure the cutter is running in the right direction -- I notice on Arc's web site it appears that only the MT2 x 1" arbor has a LH thread ?? all the others seem to be RH

Are you sure the nut is not "bottoming" on the shank thus not gripping the cutter properly - this should not happen if the mandrel is made correctly and I would think this is not the case with one form Arc. All my mandrels are home made except 1 they are mostly locked with an Allen screw and I have no problems with driving the cutter. The purchased on came from

Was there a reason you removed the key e.g. no keyway in the cutter ?

John

JasonB06/06/2019 19:52:06
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The nut could bottom out if you have removed too many spacers.

As I said the LH nut needs the spindle to run in reverse otherwise the forces will want to undo the nut.

I think ARC do 3 with LH nuts, at least that is whats in my paper catalogue.

I never use a key and don'r recall a saw slipping, infact my stub arbor does not have a keyway

Hillclimber07/06/2019 17:18:23
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149 forum posts
33 photos

Chaps, job done. Now let me explain. And thank you all for your help.

First thing I did was look for an opposing pair of flats on the arbor to allow me to tighten the LH thread nut. There is none. So decided to work with what I had.

Next then, was to reinstate the key. This helped rather a lot. Except the Morse taper then released instead (albeit at a higher torque). This was not helped by the 140T saw not running eccentrically, hence cutting on only a dozen teeth announced by the swishing noise on each rotation (about 80 rpm by the way). For this, I can thank RDG for their 'generously' sized 1" bore - maybe just 5-10thou on the diameter, but enough to render the saw reliably off-centre.

So I swapped in a 32T 3/32" saw of English manufacture (Summit) that I had. Great, except it didn't cut 3/32". And checking with a mic showed it to be about 12 thou 'thin'. Progress remained painfully slow, as I was still unable to advance the cross slide at any reasonable rate without the MT releasing.

Reluctantly, I then pulled out an old dog-driven Myford arbor that is associated with my saw table, bolted in the 140T saw, mounted it between centres, and ripped away despite the ills of that saw. This has no key, but is positively driven, and does not slip. So I then replaced the scrap I was testing all this on with my workpieces, and the job was done in 5 minutes.

Lessons? I'm pretty sure I have an old Myford milling arbor kicking around somewhere. I'm going to dig it out, make up a couple of centralising cups to hold saws of other sizes. And do it old skool in future.

Many thanks.

Cheers, Colin

not done it yet07/06/2019 19:32:21
3340 forum posts
11 photos

Operating without a drawbar? Little wonder the morse taper came loose - they are not suitable for side forces without positive retention.

Loose slitting saw, loose morse taper, so not surprising you had trouble! I find slitting saws are far better under controlled power feed - was yours? Good that you got the job done, though.

Grindstone Cowboy07/06/2019 19:49:00
124 forum posts
1 photos

I thought it had a drawbar?

" The mandrel is 2MT mounted with a drawbar, and held with a revolving centre in the tailstock. "

not done it yet07/06/2019 20:47:19
3340 forum posts
11 photos
Posted by Rob Rimmer on 07/06/2019 19:49:00:

I thought it had a drawbar?

" The mandrel is 2MT mounted with a drawbar, and held with a revolving centre in the tailstock. "

You are right. So how did the morse taper come loose?

Howard Lewis07/06/2019 21:26:55
2327 forum posts
2 photos

Glad that you got it fixed.

Firstly, NEVER use a key with a slitting saw. It is dangerous!

My ex Sentinel, Milling Instructor, at Rolls Royce, gave us this advice/instruction. I was very fortunate, walking past a machine, where a fellow Apprentice had ignored this advice, when the saw shattered. The one half, in many pieces flew up into the roof before falling down, the other half was still rotating on the arbor.

My Slitting Saw arbors are Soft Mandrels, bought fro Arc Euro, which have been turned down for a very short distance, at the end, and then drilled and tapped. A suitable recessed cap has been turned up to grip the saw. The cap is countersunk to take the R H thread Allen screw which clamps the cap to the saw to the arbor..

If I feed too fast and the saw jams, it slips on the arbor, (in the Mill/Drill) doing minimal damage.

The only problem is unscrewing the screw afterwards ti remove the saw. Invariably, this requires the cap to be brutalised with a Mole wrench to get a good enough grip to slacken it.

Howard

Hillclimber10/06/2019 12:45:47
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149 forum posts
33 photos

Just to recap, it has an M10 drawbar. But I just use a couple of knurled thumb turns on it, so it is never held too tightly. And when I say ' the taper released', I just mean that it rotated. My guess is that you can transmit quite a bit of torgue through a disc of 3/32 HSS....

not done it yet10/06/2019 13:02:50
3340 forum posts
11 photos

It must/should be tight enough to resist full motor load without turning. Turning will eventually destroy the taper, if not much sooner. Over-tightening needs to be avoided, too, as that might require excessive force to remove the MT. How it is removed can also be a factor to consider. I prefer to use wedges for removal, if appropriate, if the taper does not come free with a light tap of a soft metal-faced mallet.

One situation to avoid is placing a colder MT shaft into a warmer socket - and achieving a shrink fit situation!

HOWARDT10/06/2019 13:37:50
449 forum posts
14 photos

Always use a slitting saw under 3mm (1/8" without a key, faction between on the blade between the spacers should be enough to hold, if not too much force is being applied to the cutter. In my apprentice days on horizontal mill always removed the arbor key, it was quicker than making a new one after fessing up to the foreman.

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