making a 3″ saw-blade clamping washer with a tapered thickness

[milesincamParticipant @milesincam]

I have offered to repair for a friend a large saw-blade clamping washer that was “machined” for him by a chap using an angle grinder, when he was asked to re-face the critical arbour-bearing surface which had become galled and uneven.  As this is the face which bears on the spindle to align the blade, which is 16″ diameter, it needs to be spot on or the wobble is terrifying. The angle grinder work was NOT spot on…

I’m using my Myford ML7 for this, so very standard.

The washer is one of a pair. They are steel, 75mm diameter, about 6-8mm thick in the centre with a 25mm diameter flat portion on one side and then that outer face tapers down a couple of mm to the periphery.  The blade side is relieved in the centre with the blade-contact surface being only 6mm wide ring at the outer diameter.

I can easily put the washer in a 3-jaw chuck with the blade-contact surface as my reference on the chuck jaws.   Cutting the central bearing surface – easy, no issue at all. But then I realised that the angle-grinder enthusiast had produced a wildly uneven thickness over the whole diameter, so the washer is now really out of balance and will contribute to additional vibration – plus I can’t hand back this vile travesty as “my work” without fixing this additional issue.

The problem is – how to cut this perhaps 3-degree taper from centre to edge, when my topslide can’t be set anywhere near that angle?   I confess I’m a little baffled that Myford’s design seems so limited in in the allowable angles, is there some reason that I don’t understand?  I’ve never needed to do this angle of cut before.   Freehanding it in lots of little steps and then smoothing them off with a file would be the last resort…

Any clever members who can explain how it could/should be done on this lathe?   I can pack the part out so the working surface is proud of the chuck jaws, but I just can’t see how to progress a tool at that shallow angle using any combination of available motions.

cheers, and thanks in advance from the chap with the saw. Buying replacement washers is not easy as the spindle size is a peculiar one and they would have to be reamed out to fit. I think the saw was built ~50 years ago and is a terrifying example of DIY power tooling – a chunky and surprisingly accurate wooden frame carrying the arbour, a brutal 5HP+ 3-phase motor with DOL starting, and absolutely no guarding at all.  I was there when the 16″ blade started thrashing around in a cut and it was truly scary.  My “big” Wadkin is a kitten by comparison…

Miles (Cambridge)

[Julie AnnParticipant @julieann]

As I understand it that’s a fundamental limitation of the Myford. Just checked on my lathe (Harrison M300) and no problem setting the top slide to 3°. There are several options:

• Grind a tool to have flat face at about 3° and take a series of steps across the face of the washer. Should be straightforward to match the depth of successive cuts so little, or no, cleaning up needed.
• Borrow a bigger lathe
• Buy a different lathe (tongue in cheek!)

Julie

[John HaineParticipant @johnhaine32865]

I guess you have an ML7?  That does I think have a limited range of angles for the topslide.  The S7 has a different clamping arrangement with an unlimited range of angles.

I can’t see why the taper has any function, I think I would just make a new washer with a uniform thickness  from a short bit of 3 inch bar.  As the blade is 16″ dia no one will see the washer anyway (assuming that there’s a saw table).

[noel shelleyParticipant @noelshelley55608]

The important surfaces are the bore and the ridge face round the edge, these should be turned in one setting to maintain concentricity Etc. The angle face is largely cosmetic ? Can you not reverse the work in the chuck, space out from the jaws and set over the top slide ? you should have enough travel to get 3″od. I have an S7. Noel.

[DC31kParticipant @dc31k]

It might be too much work for a one off, but attach a 3 degree tapered wedge to the cross slide and a bearing stop fixed to the bed. Then as you traverse the cross slide, the carriage will move longitudinally. Either use hand pressure on the carriage wheel or a string and weight to keep follower and template in contact.

It is no different to a longitudinal template-follower process, just at 90 degrees to the normal direction.

Turn the screen sideways and read this post:

Lathe copy attachments

[JasonBModerator @jasonb]

Does it really need to be tapered, can’t you just turn a few even steps across the surface.

If really fussed do that then use a hand graver to blend them into a taper.

[DC31k]

On DC31k Said:

….no different to a longitudinal template-follower process, just at 90 degrees to the normal direction.

Like this:

Note the home made bracket and template on the saddle.

Julie

[Nigel Graham 2Participant @nigelgraham2]

Firstly, is that taper important to the function? If not then can it be omitted?

I’d be inclined to establish if the saw needs anything more complicated than a larger version to what is on an angle-grinder.

On these, the outer face of the washer runs in fresh air so is flat, with just a chamfered rim; the inner (clamping) surface has a shallow recess for much of the diameter so grips on a narrow annulus.

Parting-off that diameter on a Myford might be a bit brave. I have done it but not would claim the cut surface was flat.

Assuming the above conditions I’d be inclined to saw a thin billet from stock bar, or cut a disc from plate using a cylindrical hole-saw. Centralise the blank in a four-jaw chuck, drill and bore the spindle hole, bore the recess. Skim the face of the annulus to ensure it is perpendicular to the bore.

Make a simple mandrel, and leaving that in the chuck, mount the disc on it to finish-turn the circumference and chamfer the rim.

[milesincamParticipant @milesincam]

Thanks to everyone for such useful and thoughtful suggestions.  I had not ever considered the carriage-follower type of approach, that’s a useful one to remember.   The 3deg tool is also very doable and as it is not at all a critical surface (other than looking respectable) it would probably work.

I have now discovered that the original washer has some sort of laminated structure (!) and it’s coming apart, so Nigel’s recipes for making a new one might well be the way ahead.  I can get a slice of bar from Mackay’s in town, which would at least be a good start.

I recognise that Harrison topslide, same as the one I used to like at work. Not sure what the Colchester item is on the right, though…  I think the Myford design is just because there is so little height available, they gave up on allowing complete rotation.  It’s a shame – the lathe has a lot of sentimental value but it is a bit limited.  I suppose that is where the fun comes in getting around those obstacles 🙂

 

cheers all,

Miles

[milesincam]

On milesincam Said:

I can get a slice of bar from Mackay’s in town, which would at least be a good start.

When I first started with my current workshop I bought some bright steel from Mackay. They didn’t know the difference between bright and black steel, which wasn’t a good start. The bright steel was the first steel I turned on my new (to me) lathe. No matter what I tried I couldn’t get a good finish, which was really depressing. A little later, when visiting a local machine shop to discuss an aluminium box I’d designed and wanted CNC milled I mentioned my problem. Their answer was “we never buy steel from M****, it’s c**p”.

Julie

[milesincam]

On milesincam Said:

Not sure what the Colchester item is on the right, though…

It is a Hepworth hydraulic copier, also called a hydraulic tracer. Tru-trace was a US manufacturer of similar.

You may recognise it from here:

Hepworth Lathe copying attachment

On YT, Keith Fenner did a good video of his:

Can also be seen in action in the Colchester Lathes video (the background music should have been ‘ring my bell’ by Anita Ward):

[DC31kParticipant @dc31k]

As with most Myford issues, someone has been there in the past and thought of a solution.

Please see:

ML7 Topslide limitations

and the whole of the discussion in that topic in general.

[milesincamParticipant @milesincam]

Thanks Julie – what a shame that they are not a good source.  I used to buy things there, partly to support a local firm, and I do like that they maintain a good mixture of hardware, fixings, tools (less and less) and have the metal warehouse. The really grumpy old boy has retired now… and they do try to help.

Where would you recommend buying nice free-machining steel from that is nearby?  I have not looked around much as I generally try to make bits from my stock of stuff first.  But I have no 3″ diameter steel at all, nor even a plate suitable to cut a circle blank from.

thanks again for your helpful replies.  And info on your much more advanced equipment 😉

Miles

 

[larry phelan 1Participant @larryphelan1]

Just wondering, why does it need to be tapered ?

The flanges on my benchsaw are flat on both outer sides, just recessed on the inner side to grip the blade. Been like that since I bought it, about 50 years ago, and still working fine.

[Martin ConnellyParticipant @martinconnelly55370]

Simplest reason may be to reduce raw material used in a forging or casting. Taper may be something to control resonance or it may be weight reduction to reduce inertia of the blade and its mounting. If the original motor has start coils and the blade rpm is high extra inertia may result in the blade taking longer to get up to the speed where the start coils cut out. You don’t usually want the start coils energised longer than they were designed for, especially if there is plenty of sawdust about.

Martin C

[Martin Connelly]

On Martin Connelly Said:

If the original motor has start coils and the blade rpm is high extra inertia may result in the blade taking longer to get up to the speed…

And in this modern era, I believe there are regulations concerning spin-down (stopping) time when the power is removed.

—

The orignal question is about a machining technique – a method by which to cut a shallow ‘facing taper’ on a Myford with limited top-slide swivel capability.

So asking ‘why is it necessary?’ is irrelevant – the type of response required is one which would answer ‘how is it possible?’

[bernard towersParticipant @bernardtowers37738]

Isnt thaty PUWER 2000 but doesnt apply to home use

[DC31k]

On DC31k Said:

The orignal question is about a machining technique – a method by which to cut a shallow ‘facing taper’ on a Myford with limited top-slide swivel capability.

 

So asking ‘why is it necessary?’ is irrelevant – the type of response required is one which would answer ‘how is it possible?’

The best reponse is one which helps the OP. An answer limited to a direct response to the specific question is not necessarily the most helpful. If someone asked you “How do I make a hole in my head?” would you not be tempted to seek some context?

PS – How the blazes are you supposed to trim a quote on this forum without mangling the formatting?

[John HaineParticipant @johnhaine32865]

Actually this discussion illustrates an important point about solving engineering problems, or indeed problems in general.  The OP asked about how he can turn a very steep taper on his Myford – the answer is he can’t because of the topslide design.  There are various ways he might try to make a taper not requiring a topslide, but often a good way to tackle a problem is to “unask the question”, which I and others were trying to do.

So why is there a taper on the original washer?  The only real purpose that might have some validity is to reduce the moment of inertia by taking some of the mass away from the edge.  (Though in the context if a 16″ saw blade I doubt it would make any significant difference.) If you want to take mass away from the edge without making a taper you might just as well turn a step or a series of steps.  A fairly simple calculation would tell you how many steps and how big to make them.

As to sourcing the metal.  Actually even crummy steel would do this job, it mightn’t give a great turned finish but no one will see it once fitted.  I’d get Mackays to cut a slice or two of a suitable length from a 3″ round bar.  When I made a new Quorn workhead to take R8 collets I did just this (though bigger bar), to make the calibrated “thimble” to set the angle.  Finish not great but it does the job.

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