Home Made Rear Toolpost Issue

[HopperParticipant @hopper]

Posted by larry phelan 1 on 02/03/2021 09:20:16:

I have a homemade toolpost using those blades, held in place with one long bolt from the cross slide and it works OK.

Hopper, to pick your brains once again. The fingers on my steady have left hand threads, which I find confusing. Is there any good reason for this arrangement ?

Can't think of one. Weird.

[HopperParticipant @hopper]

Posted by Nigel Bennett on 02/03/2021 11:20:23:

There was a bit of correspondence in ME back in the 1980s if I recall, where some chap made a rear toolpost out of a length of 2" square RHS with a central stud. Somebody made one like it and after a bit of a dig-in was looking somewhat askance at the smashed pieces of Tee slot that used to be part of his cross-slide.

I think the same worry could be expressed about John Baron's toolpost; I don't think it would need much of a dig-in to rip it out of the tee-slot.

The one I made has three fastenings; two like David George's at the front through a fixed sub-base into a single long Tee nut, and one going through the rotational point of the "Wole Thing" (as Fred Dibnah used to say) into a substantial tee nut on another tee slot. Definitely need the long cross-slide to fit mine.

I think the problem there may be that the RHS was stood on end so the T nut in the slot was pulling the cast iron of the cross slide up into mid-air so there was nothing to stop it ripping a lump out of the T-slot. Like what can happen if you screw a clamping bolt on a milling machine table down into a T nut and let it bottom on the T slot and push the nut upwards.

The single bolt rear toolpost in my pic above has been in use for over 50 years with no ill effect. Although, its base is a good 3" diameter or so, not just the same as the vertical round column. So I don't think its the single bolt that causes the problem.

[egaParticipant @ega]

The various personal styles of parting off were nicely illustrated in an ME cartoon where I think one of the characters suffered a catastrophic dig.

Martin Cleeve, who worked his ML7 pretty hard, damaged his cross slide in the way suggested and replaced it with a steel version (I think actually produced at his request by Myford).

Clearly, there is a balance to be struck between timidity and recklessness!

[Alan JacksonParticipant @alanjackson47790]

Here is my rear toolpost. The base unit has a sloped surface which enables easy height setting without affecting rigidity and the two hold down bolts screw into a long tee nut in the tee slot.

Edited By Alan Jackson on 02/03/2021 11:52:49

Edited By Alan Jackson on 02/03/2021 11:53:32

Edited By Alan Jackson on 02/03/2021 11:55:04

[egaParticipant @ega]

Posted by Hopper on 02/03/2021 11:36:18:

Posted by Nigel Bennett on 02/03/2021 11:20:23:

There was a bit of correspondence in ME back in the 1980s if I recall, where some chap made a rear toolpost out of a length of 2" square RHS with a central stud. Somebody made one like it and after a bit of a dig-in was looking somewhat askance at the smashed pieces of Tee slot that used to be part of his cross-slide.

I think the same worry could be expressed about John Baron's toolpost; I don't think it would need much of a dig-in to rip it out of the tee-slot.

The one I made has three fastenings; two like David George's at the front through a fixed sub-base into a single long Tee nut, and one going through the rotational point of the "Wole Thing" (as Fred Dibnah used to say) into a substantial tee nut on another tee slot. Definitely need the long cross-slide to fit mine.

I think the problem there may be that the RHS was stood on end so the T nut in the slot was pulling the cast iron of the cross slide up into mid-air so there was nothing to stop it ripping a lump out of the T-slot. Like what can happen if you screw a clamping bolt on a milling machine table down into a T nut and let it bottom on the T slot and push the nut upwards.

The single bolt rear toolpost in my pic above has been in use for over 50 years with no ill effect. Although, its base is a good 3" diameter or so, not just the same as the vertical round column. So I don't think its the single bolt that causes the problem.

Assuming that the cross slide itself is flat then the mating surface of the base should be flat to match (and certainly not convex). I agree that a single bolt should then suffice and Myford's own early RTPs were made in this way.

However, in practice, perfect mating may not be achieved and the additional fastenings provide some insurance against this.

I suppose it may be permissible to scrape the base very slightly concave; the RHS design may have been an exaggerated and misguided attempt in this direction.

[HopperParticipant @hopper]

I am actually in the process of making a GH Thomas style rear toolpost for my ML7, much like the one David George shows above. It has two mounting bolts and tee nuts on the foot that sticks out. These go in the rear T slot and the vertical body of the toolpost sticks out the back of the cross slide. It looks to me, being used to my old single bolt type, that this type is more likely to pivot on the edge of the cross slide and pull lumps out of the T slot. But they have been in use since WW2 or so and seem to work ok. They just look "dicky" to me, perched out there in mid air.

[bernard towersParticipant @bernardtowers37738]

Hopper I thought that the two nuts on the foot went towards the operator, that’s what makes it so rigid!

[John BaronParticipant @johnbaron31275]

Posted by ega on 02/03/2021 11:31:10:

John Baron:

Thanks for your reply and photo.

I may be having a senior moment but this was the feature I was interested in:

I'm guessing that it may be the adjuster screw head?

I happily used a simpler version of your front tool post for many years, IIRC a Len Mason design from ME.

Yes you are right it is the height adjustment screw. I mistakenly thought that you were referring to the split clamp.

I think it must be me having the senior moment, now that I've re re read your original question. Sorry !!!

 

Edited By John Baron on 02/03/2021 14:40:31

[John BaronParticipant @johnbaron31275]

Posted by Nigel Bennett on 02/03/2021 11:20:23:

There was a bit of correspondence in ME back in the 1980s if I recall, where some chap made a rear toolpost out of a length of 2" square RHS with a central stud. Somebody made one like it and after a bit of a dig-in was looking somewhat askance at the smashed pieces of Tee slot that used to be part of his cross-slide.

I think the same worry could be expressed about John Baron's toolpost; I don't think it would need much of a dig-in to rip it out of the tee-slot.

The one I made has three fastenings; two like David George's at the front through a fixed sub-base into a single long Tee nut, and one going through the rotational point of the "Wole Thing" (as Fred Dibnah used to say) into a substantial tee nut on another tee slot. Definitely need the long cross-slide to fit mine.

Hi Nigel,

Yes I agree that there is that risk ! However I've very rarely parted off anything more than an inch in diameter, much preferring to use the bandsaw. However I did start to make a base piece to go around the column and fasten to the "T" slot in front of it. Another one of those round toit's

[John BaronParticipant @johnbaron31275]

Posted by bernard towers on 02/03/2021 12:23:40:

Hopper I thought that the two nuts on the foot went towards the operator, that’s what makes it so rigid!

+1

[mechman48Participant @mechman48]

I made mine from the Hemmingway kit; one side has an angled slot , but I found that this created too much overhang & altering it moved the centre height out of position so I used the horizontal slotted side with a different holder which allows me to alter the over hang without losing centre height..

Leaving the centre height as shown produces too much over hang..

George.

[Howard LewisParticipant @howardlewis46836]

When I had a ML7, I made a back toolpost from a piece of 2" box section, and welded gauge plate onto it to make the platforms.

From memory, it located to the Cross Slide by having dowels in the base which were a snug fit in the T slot.

For my present lathe, I made a four way indexing back toolpost. This locates to the Cross Slide by two 1/4" dowels which bear against the back of the Cross Slide. It is secured by a long T nut with two M8 studs tapped and peened into the long T nut. (IF I could find pictures of it, I would paste into an album, but can't )

So you have two methods of locating a back tool post to prevent it rotating.

Not sure if you need such a large securing stud. A 1/4 BSF stud was quite sufficient to crack a Cross Slide on the ML7! So a single M8 stud into a t Nut and two dowels should be quite sufficient.

PS  I run my parting tool with no Top Rake. to reduce the risk of dig ins! makes keepingbthe tool on centre height much easier.

Howard

Edited By Howard Lewis on 02/03/2021 16:01:07

[egaParticipant @ega]

Posted by Hopper on 02/03/2021 12:17:41:

I am actually in the process of making a GH Thomas style rear toolpost for my ML7, much like the one David George shows above. It has two mounting bolts and tee nuts on the foot that sticks out. These go in the rear T slot and the vertical body of the toolpost sticks out the back of the cross slide. It looks to me, being used to my old single bolt type, that this type is more likely to pivot on the edge of the cross slide and pull lumps out of the T slot. But they have been in use since WW2 or so and seem to work ok. They just look "dicky" to me, perched out there in mid air.

I agree with you about the look of the overhung toolpost.

However, it is worth remembering that GHT's design was probably based on Ian Bradley's earlier work. IB's design for the Drummond was I believe overhung. The explanation for why the design works in practice may be in the following point from his Amateur's Workshop:

"the attachment [is] secured to the cross slide by two T-slot [bolts] located directly under the cutting point of the tool. The location of these T- slot bolts is an essential feature of the design. The placing of them directly under the tool point is intended to overcome the tipping strain imposed on the attachment when in operation".

The longer cross slide of the Super7 does, of course, permit the third fastening passing through the main body of the RTP.

[egaParticipant @ega]

Mechman48:

Your last photo shows the angled slot; is the angle actually more than the 7 degrees in the original GHT design?

[mechman48Participant @mechman48]

It was made to the drawing supplied with kit & as I recall it was 7*. It may not look it on the pic but it was propped up at the rear so there's probably some parallax error in there… .

George.

[Anonymous]

Posted by Hopper on 02/03/2021 07:49:13:

Alignment is achieved by two round studs in the base that fit into the T slot. Just drill and ream two holes and loctite a couple of pins in there, Or tap and thread etc. You can make the pins oversize and file the final fit to get exact alignment if you like. Pins go one each side of the centre bolt. Been in use for more than 50 years that I know of and works well.

Good idea, Hopper. Better than mine for an existing part!

[duncan webster 1Participant @duncanwebster1]

Posted by Howard Lewis on 02/03/2021 15:58:52:

When I had a ML7, I made a back toolpost from a piece of 2" box section, and welded gauge plate onto it to make the platforms.

Welding gauge plate is definitely 'non preferred'. The heat affected zone can be very hard and brittle. Unless of course Howard took care to pre heat and controlled cool

[Howard LewisParticipant @howardlewis46836]

Duncan,

Sadly ignorance was bliss, so it was made from anything that came to hand. But it never cracked, fractured or distorted, so I got way with it.

Probably in my haste the heat from the first weld pre heated everything else for the subsequent ones!

The problem was getting 1/4 BSF capscrews to clamp the tool. Had to die down some ones in stock to make them into setscrews.

Howard

[Dr_GMJNParticipant @dr_gmjn]

I went with what seemed like the simplest option, which was to chew out a key in the base, and Loctite a T-nut to the stud. None of it was square, so I had to make the best of it I could. Thankfully when it's all fitted, the blade is perpendicular to the bed according to my DTI:

The boss of the T-nut just fits inside the hole. It feels pretty solid once tightened, not that I really leaned on the spanner…

There isn't much rom for the workpiece when it's fitted – presumably you just fit them when you need them, and maybe even remove the top slide to get more clearance if necessary? I've never used one before, I assume it was for this lathe since it was in the box with a home made tool post and a Myford vertical slide etc.

Still needs setting to centre height, so I guess I'll see how it goes. At least it's very easy to remove if it's junk!

Thanks all.

[Chris CrewParticipant @chriscrew66644]

It isn't junk and it should work fine by the look of it. Have confidence once it starts cutting and keep it cutting with a goodly amount of coolant/lubricant on steel. The speed should not be so slow that it 'grates' and not so fast as to make it 'scream'. Keep pulling the blade into the cut with a steady even pressure once you start. The cutting should 'hiss' just like on any other turning job. In my opinion the tip of the blade should be set a tad above centre height, but that's up to you as some people don't agree. Welcome to the Happy Parters' Club!

(PS. I use the cheapest soluble oil I can buy from the local oil merchant and dilute it 20:1 with the water added to the oil and a dash of Rocol anti-bacterial treatment. If you buy a 5L container of oil for about £20 you will almost have a lifetime's supply. It works for me, I can't speak for anyone else)

Edited By Chris Crew on 03/03/2021 02:49:45

[HopperParticipant @hopper]

Posted by Dr_GMJN on 02/03/2021 23:30:59:

I

There isn't much rom for the workpiece when it's fitted – presumably you just fit them when you need them, and maybe even remove the top slide to get more clearance if necessary? I've never used one before, I assume it was for this lathe since it was in the box with a home made tool post and a Myford vertical slide etc.
wi

Hence the popularity of the offset type with the foot sticking out the bottom and two bolts, as posted by David George above. It moves the toolpost back a good inch and half or more when you take the smaller turret into account too. You can leave those in place permanently and swing the blade around to one side out of the way. But the single bolt type really needs to be fitted and then removed each time, and yes toplside may have to be removed for large diameter jobs. That's why Im in the process of making the offset version. The single bolt one is ok on my old Drummond but cramped on the ML7. But its a quick one bolt job to take on and off so no big problem.

You might want to replace that brass nut with steel or it will eventually strip from the torquing of that central stud.

Edited By Hopper on 03/03/2021 05:39:16

[Dr_GMJNParticipant @dr_gmjn]

Thanks both.

Hopper – I liked the look of the brass nut!

Its way bigger than the M6 thread in the T-nut at the bottom (you can see the diameter difference in the second photo), and a much coarser thread. It might look huge, but it’s not in proportion to the torque that’s going on it.

Ill look out for a steel version anyway.

Cheers.

Edited By Dr_GMJN on 03/03/2021 07:42:30

[Ron LadenParticipant @ronladen17547]

I think adding the key and Loctite the stud to the T nut was the easiest option, should work well. Do you have a driven crosslide on your lathe if so that helps or at least it does on mine, you have a consistent feed and free hands for adding cutting oil etc.

[HopperParticipant @hopper]

I dont know that the 6mm thread on the bottom will be up to the job either. Time will tell I guess.

[Dr_GMJNParticipant @dr_gmjn]

Posted by Hopper on 03/03/2021 08:54:07:

I dont know that the 6mm thread on the bottom will be up to the job either. Time will tell I guess.

You said previously there was no need to drill another hole, and since I can't get a larger thread than M6 in the T-slot, that's what I'm stuck with for a single bolt.

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