Wobbly slitting saws

[lfoggyParticipant @lfoggy]

I've recently purchased two slitting saws from different well known UK model engineering vendors. Both were 4 inch in diameter with a 1 inch bore and widths were 2.5mm and 3/32. Both saws were significantly out of true when rotating, one by 0.9mm and the other by 0.5 mm. My arbor has a negligible degree of runout so the problem is the bore of the saw is not concentric with the periphery. That degree of eccentricity means that they only cut on a small proportion of the teeth. Useless really.

How can this degree of inaccuracy even happen in the manufacturing process? I would have thought the blade is mounted by the central bore for the final grinding of the teeth…

Anyway, they were inexpensive saws at less than £10 each so maybe this is a case of 'you pays your money and you takes your choice'. All the other saws in my collection come from old UK made stock and run perfectly true. Industrial suppliers charge 3 to 5 times more for new sliiting saws but maybe thats what you have to pay?

[lfoggyParticipant @lfoggy]

[Nick HulmeParticipant @nickhulme30114]

Buy cheap, buy twice (or more)
Or true them up and make a new arbour.

[Anonymous]

Why bother investing in expensive grinding machines when the saws can be "finished" by hand and still sell?

I don't know which vendors were used, but I'm very selective about which ME vendors I use. Most of my cutting tools are bought from industrial suppliers. An exception would be premium items from Arc.

Andrew

[Ron LadenParticipant @ronladen17547]

I have two slitting saws a 1.00mm and a 1.5mm and they are probably in the price range you paid, possibly the same supplier. Both of them have a 0.5mm run out which is obviously not ideal but I have to be honest both of them work fine, I have had no issues at all cutting with them.

Ron

[not done it yetParticipant @notdoneityet]

Ahh, so not cutting a wider slot than design. Eccentric rather than wobbly.

That’s OK, – well par for the course – as many cheap slitting saws only cut (to the maximum depth) on part of the circumference. Look on it as paying the same as a better quality item which uses (and wears) rather more of its teeth than yours. On yours, some teeth will be cutting and possibly some only rubbing (which blunts them quite prematurely). So likely good enough for a single job but not so much longevity, if used regularly and/or often, than a higher quality one.

The wobble saw I used cut a slot from blade kerf to about 10mm wide, depending on how it was set.

Likely need an eccentric arbor, with appropriate run out, so the saw can be turned to accommodate the eccentricity. Don’t think I would bother.

[Michael GilliganParticipant @michaelgilligan61133]

This very recent thread might be of interest: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=142966

'though, inevitably, there was no definitive conclusion.

MichaelG.

[lfoggyParticipant @lfoggy]

Thanks for the comments. I couldn't be bothered to return them so I used a carbide tipped boring bar to relocate and enlarge the bore to 26.5mm. Made another arbor out of an R8 blank I had and they now run very true and cut ok. I suspect my 26.5mm arbor will come in useful again sometime.

[Michael GilliganParticipant @michaelgilligan61133]

Nice one

MichaelG.

[WatfordParticipant @watford]

On the subject of slitting saws I am having difficulty sourcing a very small example. I need a 1/2" dia. x 1/16"wide saw to produce a key-way in the crankshaft of a Channel Island Special 10cc. I require to get up very close to the crank web without marking it.

Can any kind soul point me in the right direction, please?

Mike

[EmgeeParticipant @emgee]

Mike

You could make a cutter from Silver Steel and harden it before use, for a 1 off or a few shafts it should be OK.

Emgee

[pgk pgkParticipant @pgkpgk17461]

Posted by Watford on 29/06/2019 22:11:17:

On the subject of slitting saws I am having difficulty sourcing a very small example. I need a 1/2" dia. x 1/16"wide saw to produce a key-way in the crankshaft of a Channel Island Special 10cc. I require to get up very close to the crank web without marking it.

Can any kind soul point me in the right direction, please?

Mike

That's a tiny diameter. Have you considered some sort of dental bur presented at an angle? The problem is the obvous one of controlling the thing but if you have a compressor the high-speed handpieces and burs aren't that expensive but creating a fixture to hold it would be entertaining.

pgk

[speelwerkParticipant @speelwerk]

Posted by Watford on 29/06/2019 22:11:17:

On the subject of slitting saws I am having difficulty sourcing a very small example. I need a 1/2" dia. x 1/16"wide saw to produce a key-way in the crankshaft of a Channel Island Special 10cc. I require to get up very close to the crank web without marking it.

Can any kind soul point me in the right direction, please?

Mike 

Fraises & Outils SELECTION SA, Zwitserland, https://guye-outils.ch/presentation.php?lang=en  nr. 500.0121705 has a diameter of 12 mm but thickness of 1.70 mm. They probably will alter the thickness for you if you ask but will be costly. Alternatively you can clamp a thickness of 1.00 and 0.55 mm together, it will create a wobble but not much because of the small diameter, probably around 0.02 mm. But you have to try first to determen if it is OK. Niko.

Edited By speelwerk on 30/06/2019 00:19:45

Edited By speelwerk on 30/06/2019 00:20:30

[Chris TriceParticipant @christrice43267]

I'll probably get vilified for sounding like a broken record but I've found the cheap import ones are the worst offenders by far. I usually end up making a wide arbor to grip the cutters nearer to their periphery but of course you lose cutting depth.

[JasonBModerator @jasonb]

Watford, can you not use a 1/16" x 1/2" woodruff cutter, I've used this type of cutter to put keyways into IC engine crankshafts. You want a No204

Edited By JasonB on 30/06/2019 07:01:54

[WatfordParticipant @watford]

Thanks Jason, you are indeed a star. I was missing some lateral thinking – not unusual for me.

Working on an original Jensen kit, purchased in 1949 by a now deceased friend. Rescued from the top shelf of his workshop, and which had had very little work completed.

Mike

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