Home Made Rear Toolpost Issue

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

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

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.

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

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

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

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.

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.

I was thinking of a T nut with a larger thread, more like 8mm or the full width of the T slot which might be about 3/8 from memory. Pretty much the biggest thread that will fit through the T slot. Using the more square type T nuts. You could mill up a longer one to fit your T slots and drill and tap it to fit a thread just slightly smaller than the T slot narrow part. Make the T nut as long as the width of the toolpost base for maximum strenght. .Or a bit less so you can keep the end sections of that locating tennon you machined on the bottom for location purpose.

Edited By Hopper on 03/03/2021 09:20:17

I think what I'd do is just mill a horizontal slot along the front of the block and use one of the clamps I made for the milling vice. That would stop the front lifting, and would be a very simple addition, if it's necessary.

! Your toolpost looks to be sturdy and rigid, and well located.

GOOD! Rigidity is like cleanliness, next to Godliness.

Don't worry too much about a M6 thread exerting enough force. It is a fine thread and so capable of delivering aPossibly it will crack the Myford Cross Slide before the thread strips, if you apply enough torque!.

Screw threads are intended to provide a big mechanical advantage. Think how you can lift a car with a comparatively small diameter thread in the jack! A thread is only a long lever wrapped around a bar.

(Compare how far your hand travels in comparison with the distance that the load is lifted. )

Howard

Thanks Howard. I think the potential issues here are the quality of the thread I put on the end of the stud, and the small surface area over which the load is applied to the underside of the T-Slot.

But the clamp I have in mind should address those issues. I'll post an image in a while.

This is a milling vice clamp - It should just fit once a slot has been milled:

Well the clamp will help obviously help but since you have fitted the T nut and milled the key have you not tried parting to see how it performs..?

Edited By Ron Laden on 03/03/2021 13:50:18

You can always make an elongated T nut so that although the load is applied in the centre, it will be applied along the length ofn the T nut and the T slot in the Cross Slide. The Base of your toolpost will take the load, so that it is unlikely that a small T nut would pull through the Cros Slide, unless some MAJOR disaster happened.

I've loaded a picture of the one that I made to secure my Four Way Indexing Back Toolpost into my Album.

AS I've said the parting tool is mounted at horizontally at centre height, and has no Top Rake..

For deep parting cuts, a gravity drip feed of soluble oil is used. The fluid drops onto the tip of the tool, or on deep cuts into newly produced groove. The shop made jet and needle valve mounts on a short vertical stud in a small magnetic base.

This helps the swarf to fall away rather than build up in the groove.

Howard

Advantage of the hold down bolts in front as per GHT design is that the bolts are right under the load. This reduces the bolt load and hence the load applied to the tee slot

The other option would be to ditch the M6 nut and your stud an use a 3/8" tee bolt instead.

I think whoever made the original stud tried to use the full width of the slot, but for some reason decided to peen it in place. I’ll try to find a suitable T bolt.

If anyone is interested, have just posted another couple of pics of the 4 way back toolpost into my album, showing the locating dowels.

The central clamp stud was 10mm only because I happened to have one lying about

Howard