QC Toolpost

[Phil H1Participant @philh196021]

Some time ago at a ME exhibition I bought one of these quick change toolposts. I knew that it would not fit my Myford Super 7 but I thought it would be relatively easy to modify by opening out the central hole.

I am just a bit puzzled by the other hole. I find that the dovetail slot clamp twists significantly when it is loose. Is there supposed to be a dowel in this 'split' hole to prevent the clamp from twisting excessively in use or is the clamp fine as it is?

Phil H

[Phil H1Participant @philh196021]

[egaParticipant @ega]

At first I thought the hole was for stress relief but on looking more closely is it for a pivot?

[Phil H1Participant @philh196021]

Ega,

I also thought it might simply be to lose a possible sharp corner and or help with the manufacturing process.

I will open up the hole and have a go at using it. The twisting might be reduced when the whole block is clamped onto the top slide. I just wondered whether something had fallen out of the box.

Phil H

[jimmy bParticipant @jimmyb]

There should be a dowel of some sort and the clamp pivots on it.

Jim

[BazyleParticipant @bazyle]

You might consider turning it upside down. If you think of the direction of forces when facing and most cutting it is currently against the add on piece and the screw thread.

[Phil H1Participant @philh196021]

Thanks Jim, very helpful.

Bazyle, do you mean that the horizontal cap screw should face away from the operator rather than towards the operator?

Phil H

[Chris Kirby 1Participant @chriskirby1]

It's definitely missing a dowel, I have one I bought at one of the shows maybe twenty years ago. Came with one holder and I bought two extra. When I got home all three holders must of been machined in different centuries! One fitted, one fitted almost sort of and one didn't fit at all! Tossed the lot in a box under the bench and for all I know they are still there!

[Tony Pratt 1Participant @tonypratt1]

Posted by Chris Kirby 1 on 24/07/2020 21:06:45:

It's definitely missing a dowel, I have one I bought at one of the shows maybe twenty years ago. Came with one holder and I bought two extra. When I got home all three holders must of been machined in different centuries! One fitted, one fitted almost sort of and one didn't fit at all! Tossed the lot in a box under the bench and for all I know they are still there!

'Made in China'

Tony

[Phil H1Participant @philh196021]

Chris,

I think we both bought from the same stall. I've had mine for at least 7 years. But I think I got the better batch because as far as I can tell, all my tool holders fit ok but I will double check. If I get mine working – I might grab the holders off you (if you can find them)?

Tony,

Yes more Chinese stuff. The great shame is that they are nearly always about 80 to 90% ok at half the price or cheaper but every single Chinese thing I have bought needs 'work'. Even my simple, straightforward DTI magnetic bases need to be rebuilt. If I buy Chinese, I always consider it to be a 'kit' rather than a finished item.

Phil H

[Tony Pratt 1Participant @tonypratt1]

Phil H, Yes I totally agree with your comment '80 to 90% ok at half the price or cheaper but every single Chinese thing I have bought needs 'work''. I like most people buy Chinese stuff.

Tony

[Chris Kirby 1Participant @chriskirby1]

Phil,

I can find two of the holders you're welcome to. I seem to recall the problem was the dovetails were all machined to different sizes but you could maybe do something with them, PM your address and I'll pop them in the post.

I agree about Chinese stuff, as long as it's cheap enough it's often o.k after a bit of reworking!

[Oven ManParticipant @ovenman]

Posted by Tony Pratt 1 on 25/07/2020 10:38:42:

Phil H, Yes I totally agree with your comment '80 to 90% ok at half the price or cheaper but every single Chinese thing I have bought needs 'work''. I like most people buy Chinese stuff.

Tony

This is so true. It does seem to me that the Chinese are better at electronics engineering rather than mechanical engineering. Nearly all the assembled printed circuit boards I have purchased from China have been spot on but the mechanical bits do seem to require that extra bit of work. I actually quite enjoy stripping kit down and cleaning it and modifying it to my own satisfaction.

Peter

[Clive FosterParticipant @clivefoster55965]

That style of tool post doesn't necessarily need a dowel in the hole.

Accepting that the clamping geometry is inherently unsound the system can either be made to pivot or come up tight when the flat surfaces parallel to the opposite side of the post come almost into full contact when locked.

In the first case a dowel in the hole provides a pivot point.

In the second case its important that there be no corner to pivot of at the junction of the two faces hence the hole. Considering the action of a system with a separating spring under the locking screw its clear that as the lock is tightened up the virtual equivalent of a pivot point slides along the flat faces as the angle reduces. Theoretically, for best performance, the virtual pivot should disappear into the dowel hole before full lock is achieved.

It is perhaps instructive to consider the exact angles of the dovetails and accuracy thereof needed for theoretically proper operation of either version. They are clearly required to be different.

Clive

Edited By Clive Foster on 25/07/2020 12:25:20

[Phil H1Participant @philh196021]

A quick update;

I opened the central hole up to fit the Myford Super 7 toolpost stud and tried the 'system' as it is (without a pivot pin). It seems to work quite well so far.

Phil H

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