Mini Lathe 4-way toolpost

Does anyone happen to know what the standard mini lathe toolpost is made of?

To this non expert eye it looks like it's not steel but some grade of cast iron?

Reason i ask is i want to make a new one to take up to 1/2" tools.

This will make the base thinner but not so thin, as due to my non informed & later more informed attempts to get the topslide working snug & smooth i've lost some height on the topslide. A 7/16" tool will almost fit to centre height as is.

The topslide does actually work quite well now!

The loss in base thickness will be offset somewhat by making it a two way toolpost, so there will be some additional side bracing not present on the original.

Material options are Ali (we can chuck that one out i think, ) , Steel, Cast iron, Or S.G Cast Iron.

Any thoughts? I'm thinking standard Cast Iron may not bare up too well the way i torque down the tool retaining bolts!

This will give the micro mill a good workout cutting the slots , but i'm not proposing to cut the slots full width in one.

Thanks.

Steel is widely used for toolposts. Less likely to crack under the pressure of the clamping screws. Cheaper to buy and cleaner to machine too.

Steel will be fine, some thing like EN32B, made one years ago for my Unimat 3 on the Unimat 3.

To save the mini-mill consider packing up your block on the cross or topslide and milling on the lathe

Unless you already have some 12mm shank cutters it's probably not really worth it

" ... the way i torque down the tool retaining bolts! "

Errrr..... you do realise you admit being excessively heavy-handed with your machine-tools? And I do not believe you are using any torque measurement with it.

The retaining screws need be tight, but not so tight they risk damaging anything.

No need to overtighhten trhe clamp screws.

A screw thread can produse an enormous end load.

Think of the thread as a lever. If one turn lifts a load by 0.1" and the handle turning the thread is 10" long, the Effort has moved just more than 31" to move the Load 0.1" That is a mechanical advantage of over 310 :1

So a quarter turn of a M8 screw moves 0.3125 mm Quite a load imposed for very little effort.

If the ends mushroom, youn are overtightening and laible to crack a toolpost made of cast iron.

At the corner of the tool slot you are subjecting the metal to tension. And cast iron is not strong in tension.

You will even delfect a steel toolpost.

No need to yield tighten!

Howard

Thanks for the replies all.

@ JasonB ~I've a box of used mo max 1/2" somewhere under everything else, can't do anything with them currently.

@ Nigel G, not a trained engineer,so sometimes do not use the correct engineering term. "torque down" the bolts is just a common (mechanics?) expression to me.

Actually i could try using the torque wrench to get an idea of whether it really is abuse! Generally i have a light touch with things all mechanical.

The reason I tighten these bolts well because i note by the time it comes to change tools only very light pressure releases the bolts so maybe something is amiss?

Don't worry Howard, i haven't mushroomed anything~ not sure i'd have the strength these days, more 'Mr Muscle' than 'Mr Universe'

As i've already got some suitable steel stock maybe i'll go with Hopper & Jason's suggestion rather than buy something in.

I made one for my old Drummond out of plain old bright mild steel, 1020 grade here not sure what the UK code would be. Milled it in the lathe as Jason suggested, after removing as much metal as possible by drilling holes in the slot area using the drill press. Makes the milling go quicker on my shaky old Drummond. It does not like heavy milling due to its small spindle diameter I think.

Edited By Hopper on 04/03/2023 08:41:34

I think probably most of us have, and don't..

.

An interesting ambiguity in the use of language ^^^

To me … ‘torque down’ would imply the use of a torque-wrench, specifically to consistently achieve the appropriate tightness of fixing.

… I suppose it depends how one was “brung-up”

MichaelG.

Back in my SouthBend driving days I made a number of 4 way toolposts from standard stock sections. Don't recall the exact details but I think 1/4" or 3/8" steel plate for the base, 1/2" plate for the top and, probably, 1" or 1 1/4" alloy bar for the middle. Screwed and glued together using either M5 or M6 countersunk hex socket screws and one of the Loctite construction adhesives.

Design was fundamentally based on what I had or could scrounge. Alloy is plenty strong enough fro the centre part and far easier to tap. My then boss called me several rude names prefixed with "cheating ..." as he'd recently carved two from solid for his Boxford. Which seemed far too much like hard work to me.

Don't leave the base flat. Put a shallow recess of diameter around half the block width in the centre. This ensures altho the hold down force is applied to the outside of the block where it has much more mechanical advantage against twisting. A flat base is likely to mostly hold close to the middle so needs to be held harder ton stop twist. A "gasket" of thin card or soft aluminium spreads the load and improves grip. Need to change a card gasket every year as it picks up oil.

Were I to make more I'd do two slot blocks rather than four ways. Four way ones have undesirable porcupine tendencies and, in my experience loading more than two tools tends to be inconvenient. If you intend to use interchangeable tip carbide tools set the base thickness so you don't need shims.

Clive