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

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