Mini Lathe Rear Tool Post

My Sieg C3 (mini lathe) now uses an "oxa" QCTP also acquired from Arc Euro. The square, flat, spacer went straight into the "small bits" bin no doubt to return to dust there. Most of my tooling has 10mm x 10mm shanks Some time (years and years) ago I made a post and clamp, Norman(??) style toolpost (look in my Albums). This used an upside down parting blade, and obviously required the spindle to turn in reverse. Being a modern machine with a bolt on chuck, this caused no problems with the chuck unscrewing. Parting off with this set up was a breeze. Although parting off with the oxa is o.k. there are still knuckle whitening moments, I'm thinking of making a toolholder with an upside down blade, to try and improve things

I recently nearly finished a "chariot a vis" (Schaublin terminology) for a Schaublin 70 (again, look in my Albums). All machined on a 10 or so year old Sieg X2 mill. Gordon Bennett what a mess, but it does machine beautifully. Because my new chariot does not get used very much on the Schaublin, it occurred to me that for the small things that I make quite a lot of, The "chariot a vis" could be used on the Sieg C3 (after removing the carriage obviously). We shall see!!

cheers

Bill

Hi Bill, your note about the "chariot a vis" triggered a memory, but it's not related to Shaublin or Sieg lathes -

A old shop instructor of mine, from the east end of London, was always saying "Wot vuh flamin' 'ell is vis?" when looking at something we just set up, or finished. He was a master craftsman, we had to work hard to even approach his required standards or work. He taught us a great deal about the technical side of things but also about survival in the work world. I miss him.

(I don't think Shaublin had this usage of "vis" in mind when describing their 'screw carriage'

Edited By Jeff Dayman on 14/02/2019 21:14:40

The new cross slide is finished, well apart from a good clean up, debur the corners and edges and I am going to polish the dovetails and underside running faces with some 1200 paper.

I ran the top of the Tee slots full length but the lower section of the slots stop short front and rear of the turntable. Just the top slide to modify and it can all go back together.

Looking good, Ron

MichaelG.

Indeed. Ron deserves a prize for being 'the man most likely to'. He's gone from beginner to 'gosh' really quickly. If only I had half his talent. Bet I could out bodge him in a contest though, bodging is my specialist subject...

Thanks Michael/Dave

Dave, I dont know about talent when it comes to model engineering, some of the stuff I see on here is way beyond me. Bodging however is right up my street, give me some contact adhesive, duct tape and a pack of cable ties and I am in my element...

Ron

I have reduced the height of the top slide by taking off 5mm from the tool post seat and loosely placed all together just to check dimensions. Although the heavier cross slide has lifted things the top slide reduction plus changing to an ARC 000 qctp puts the tool 12mm lower/closer to the base of the top slide assy. I,m hoping that this will help towards improving rigidity.

With the extra thickness of the cross slide the turntable mount drops down and sits on the saddle face whilst conveniently retained by the mount hole so it slides back and forth with the slide. Using the cross slide with the top slide removed I can see a problem with swarf dropping in and getting through to the underside of the slide so I thought of turning up a nylon plug which drops in and prevents any ingress, should work.

Well its all back together the heavier cross slide fitted adjusted and set-up. Will it make any difference though..? well its early days but it does feel different, this could be my imagination of course but hopefully not. I did a number of parting offs with alu and steel and that certainly has changed for the better. I inverted the tool and ran in reverse, the first time I have tried that and had no issues at all, in fact it was a pleasure to do. Whether the improvement came from the inverted tool or the heavier slide I dont know but I suspect a combination of the two.

I am impressed with the ARC tool post, looks to be well made and good quality, works well too. Out of interest I clocked the tool holder after removing and refitting half a dozen times and it was spot on, so I guess a good sign. Despite getting an improvement with the parting I,m still going with a rear tool post which was the main reason for the new cross slide. So thats enough for now in the way of mods to the lathe (and the mill) there is a 0-4-0 waiting for a few finishing jobs and an engine I started and need to get back with.

Ideally I would like to make the rear tool post from cast iron, it will mainly be used for parting off so once the tool is set up it wont be removed from the post that often apart for sharpening. Cast iron is a new material to me and was wondering if the clamping screws which hold in the tool holder would need threaded inserts or if they would be ok just threaded in the cast iron itself, the thread length will be around 20mm deep.

The other question I guess, would steel be preferable for a rear tool post.

Ron

Every now and then my old employer drags me out of retirement and this week I have been working at a large engineering company.

Before I left and thinking of the rear tool post I asked if they had a short piece of 50 x 50 steel I could buy plus would they allow me to have a look in the scrap bins for any ends or small offcuts. The production manager said the bins had been emptied the day before but they would see what they had around the shop.

Just before I left they gave me a box containing a selection including a 75x50x50 piece of steel. Despite my trying the manager flatly refused to take any payment. I will be going back and I think a very good bottle of something nice will be the least I can do.

Edited By Ron Laden on 28/02/2019 19:15:44

I have machined and squared up the basic block for the rear tool post but I,m a bit undecided which way to go forward.

The main use of the post will be parting using a 2mm tool which I need to make a holder for, I did think of machining a tenon on the bottom of the post which would locate in the T slot and fixing the post to the slide. Would it be more versatile to go with a mount each side of the post, one for the parting and one for other tooling and have the post swivel, havnt quite figured out how to do that though.

The post is 50 x 50 and it does look a bit large on a mini-lathe, wondering if 50 x 40 or 40 x 40 would be better.

Edited By Ron Laden on 03/03/2019 10:41:45

In addition to grounding severe cutting forces better by being positioned at the rear the major advantage of this type of tool-post is its extra rigidity. Any bending and vibrating during parting off are bad news. I'd do everything to enhance the posts rigidity (like adding a tenon), and nothing to reduce it (like having it swivel, weakening it by cutting rarely used slots, or by reducing size and weight.) Rear tool-posts excel at parting off and I wouldn't spoil one by squeezing in other features that might reduce its stiffness in any direction. Unless you have something particular in mind?

Dave

Ron Laden:

Have you looked at the Duplex/GHT/Hemingway style turret?

Will you use it solely with the tool up side down? Obviously, this affects the location of any slot for the tool.

Myford's early RTP had a tenon and single bolt fixing. A step might permit an additional holding down bolt:

The picture also shows a simple way of holding the parting off blade.

Dave,

At the moment I am only thinking of parting so you are probably correct in maintaining the posts size and adding no bells and whistles which could compromise rigidity.

Ega,

Yes I was thinking of using the tool upside down and thanks for the picture of the tool mounted direct to the post. I was wondering if there was a way of avoiding a tool holder and that looks a good way of doing it, I should imagine that is quite rigid.

Ron

SOD makes a good point about rigidity and I suppose the rotating turret does raise the possibility of some loss of it; both my RTPs are like this and seem to work well, however. You could make it one-piece to start and go with a turret later if it seemed desirable.

The direct mount slot does, of course, need to have angled top and bottom to suit the tool.

Hi Ega,

I do like the idea of having the parting blade mounted direct to the post. Unless I,m mistaken your post appears to have no vertical adjustment, not a problem with an insert tool as you are using, changing the insert will maintain the tool height. However I plan on using HSS tooling so a bit more tricky maintaining the tool dimensions when sharpening but I could always make up a small jig.

Re the angled top and bottom mount slot, I am assuming this creates a shallow dovetail which pulls the tool in when nipped down..?

Ron

Ron

Yes, I am relying on the consistency of the insert to maintain centre; I'm still on the first of ten ISCAR brand items and feel these should be within a thou or so. The initial adjustment was, of course, set by facing the under side of the turret. In principle, I think the same approach could be adopted for a conventional HSS blade set level with zero top rake.

In the GHT post I have on the Myford, however, the slot is angled at 7 degrees and the projection is then varied to set the height.

In either case, as you say, the idea is that the tool is retained by the shallow dovetail, (8 degrees in the GHT turret).

Congratulations, BTW, on your cross slide and good luck with the RTP!

Thanks for the detail Ega, that is helpful.

Ron