Home Made Rear Toolpost Issue

I realise that may just be illustrative, but that seems a lot of overhang for easy parting off.

Neil

Thanks Howard.

Thanks Neil, it was purely to show something along the axis of the chuck to show the clearances with a typical workpiece. I wouldn't try to part anything off as it's shown.

Hi Guys,

I perceive one problem with all the rectangular rear toolposts !

That is ensuring that the tool is dead nuts parallel to the chuck ! Any slight miss alignment in the positioning will cause parting issues. Here I'm talking about angular and or rotational alignment.

I checked it with a dti - its fine. The key in the base has the advantage that it's repeatable too without having to re-set everything when fitting.

The one I made just requires lining up with the cross slide when the bolts are tightened and it is dead square.

The base plate on my tool post has 4 dowel pins which locate in the two T slots for alignment on the cross slide. I always sandwhich a piece of 10mm square tool steel between the parting blade and the face of the chuck as a quick check that the blade and holder is sitting square.

Edited By Ron Laden on 05/03/2021 07:08:40

Edited By Ron Laden on 05/03/2021 07:09:52

Thanks Ron, that’s a good idea. I’m hoping my 3/8” T bolt arrives today, so I can give it a try.

So I milled the key to clear the new bolt:



and set it up using the "against the chuck" method suggested earlier in the thread:



I tried it on some steel, and then some brass. It was "OK", but in no way was the step change I thought I'd notice having read about the improvements to parting this should give. I thought I noticed some movement, so I went ahead and milled an extra slot in the block, for a clamp, which fitted perfectly:



I then tightened the bolts after setting against the chuck again, and...something felt wrong. Surely not a stripped thread?

No:



This really sums up for me the utter misery of making tooling - I spend hours fettling something, for it to fail. I suppose I should have investigated further why it was in a box in the first place - and the out of square on the faces should have prompted me to treat it with more suspicion. I think it may have been cracked already, and using it for the first time yesterday propagated it a bit, then re-tightening it was the final straw.

I'm having no luck at the moment at all with trying to fettle my equipment. Even the leadscrew nuts I was sent for the slides didn't fit, and I'm having to modify them. I'm not sure if this happens to anyone else, but sometimes I can't make any progress, and it would be easy to give up and just sit and watch telly. That's two weekends' worth of free time wasted on various dead end projects in the garage.

So, undeterred - for now - can anyone recommend a rear toolpost for an ML7, and also a good parting tool? Please don't suggest making one - I have less than zero interest in making tooling, I just want to buy something that works.

I am sorry that you have suffered this failure, but please don't give up because (only speaking for myself) we all have disasters and learn from them. Also, you are not alone in having to make things fit, it's part of my workshop activities and consider myself lucky that I have the necessary equipment and a little bit of skill to be able to do this. If you are not prepared to splash out on a OEM Myford rear tool post I would suggest that, unless someone has another type to sell you or Ebay is not forthcoming, then your only alternative is to make one. I would copy the Myford myself because, although I am a great admirer of GHT as a mentor and guide, I am not so enamoured of his designs which always seem to me to be lightweight and lacking substance. And before anyone takes a shot, I am not setting myself up as knowing more than the great man himself. It is just that as he was such a superb craftsman I always imagine that his tools were always super sharp and so perfectly honed that they needed very little force to effect a cut. A state of perfection I have never been able, and never will be able, to achieve!

You can copy the the ML7 rear tool-post easily enough, I copied a Colchester rear tool-post out of noggins of mild steel and it works perfectly well for me. In fact if you are anywhere near the middle of Lincolnshire I have more than a lifetime's supply of suitable noggins and you are very welcome to collect one. One thing I would say, again only as a personal opinion through experience and not withstanding the crack in your tool-post, is that if something is going to hold and grip securely, it will do so with not much more than a 'nipping-up' and will not require any excessive heaving on a spanner or allen key. How many tee-slots will have been broken out by excessive tightening by people thinking that this will stop a work-piece or tool shifting? A soft card gasket usually cures a tendency to shift under most cutting forces but if it doesn't you should be looking at other ways to secure a tool or work-piece.

Edited By Chris Crew on 07/03/2021 18:45:17

Thanks Chris - giving up because of a setback isn’t really an option, but sometimes...bloody hell I feel like it! Not sure whether the Gods of ME on here have these days...

By the way I think this thing was made from cast iron. If I’m forced to make another (and let’s be clear it’s a last resort), what material should I go for?

The Arc Euro insert type parting tools look substantial - anyone got one?

Thanks all.

Hi Dr_GMGN how about just making a top plate to clamp the blade similar to my one. It looks like it would make similar and you can then slide the blade in or out to suit the job to part off.

David

For my two-pennyworth, mild steel does for most jobs probably simply because I acquired a mountain of the stuff when my erstwhile employer closed its tool room and workshop a few years ago and it is very easy to work with. I have made most things out of it even where other materials have been specified. Of course, it would not do in industry or a professional environment, but in the home workshop where sliding or rotating parts are not in use eight hours a day, five days a week, it is very unlikely that it will ever wear beyond use. The only things that I use higher quality hardening steel on are, obviously, home-made cutting tools. The Colchester rear tool-post I copied is made out of mild steel and works fine for me.

A mild steel top plate will be fine, using cast iron on the original toolpost was bound to end in tears.

Tony

Bad luck with the holder, I have mostly used mild steel, or sometimes EN24T / EN19T if there was a need for extra strength.

The supplimentary clamp would indeed improve the stiffness. Could you see if a rear lock for the saddle is feasible?

Edited By old mart on 07/03/2021 20:07:00

David, there is actually a slot machined in the other side:



It's too shallow for the Sandvik tool, and I did want to use it because it's easier to move in and out. How do you set/adjust centre height though?

I could easily enlarge the slot, but I assumed I'd need a profiled milling cutter to form a taper along the lower edge?

So slice the top off the original block and use it as a clamp? Not sure what the two grub screws were for?

I honestly don't know how these holders work, but I'd be willing to give it one last go, since I've messed about buying a t-bolt and milled the slots etc. (and it looked quite nice up to the cracking disaster.

Thanks.

What do you mean by "rear lock"?

Yep. This was inherited when I got the lathe. It's been in a drawer since 2007, so the material was selected for me.

Hi Dr_GMJN

Your picture shows beautifully crack propagation in cast iron when under tension. Cast iron should always be under compression loading.

If the top plate was steel then that would be a better material.

I enjoy making tools in my workshop as long as they are well designed and fit for purpose. Anything designed by George Thomas that I have made has been worth the time spent making it. I suggest looking at the myford rear toolpost sold as a kit by Kirk at Hemingway Tools. It's not a huge project but worth considering.

I totally empathise we you about wasted time in the workshop, it happens to all of us but you still gain experience from these set backs.

Regards

Derek