Quick change toolpost

Edited By petro1head on 13/10/2018 18:36:10

I mentioned in the parting thread that I have solved the problem of not being able to lock the carriage due to the DRO

WooHoo, 500 posts

I am not dissing the Dicksons design just I feel my post may be of inferior quality

I have found two issues when trying to fit some of the imported holders to my original post and both stop theholder locking firmly to the post.

The first is the easiest to cure. The holder should only be making contact with the two "V" sections at the end of the holder and there should be a gap where the "tee slot" is drawn in towards the post, in the photo you can see a 0.015" feeler gauge in there.

On some holders the holder makes contact where the feeler gauge is before the ends do so the holder will wobble about. Easy remedy is to hold these surfaces against a linisher or belt sander to thin them enough that they no longer make contact first.

The other problem is that the inside edge of teh "tee slot" is too far from the post which prevents the cam actuated clamp from rotating far enough to get it into the sweet spot where it holds firm. This photo shows how far the clamp rotates on an original holder

And this how far on a thick one, probably 50-60 degrees less

This shows where the problem is, original holder 0.127" and import 0.142"

Not such an easy fix and it will depend on how hard your particular holders are, ideally a carbide ciutter but at a pinch a sacrificial HSS one can be used to get under the tee to thin it down.

Edited By JasonB on 13/10/2018 20:20:54

The tool holder in the video looks like it's set in its very lowest position, causing the 'piston' to bear on the upper end of the tee slot. Is this causing the problem?

Maybe a shorter body block would bring things into line better.

Interesting, while you doing that I had a check and compared two holder and found this

The top photo is the parting off tool holder, the second is the boring bar holder.

So it looks very similar to what your saying and would explain why I have been having parting problems as the parting holder is not being properly clamped.

So i need to study you photos and do some measuring and machining

Thanks Jason

I believe the problem is where I have arrowed in yellow is wider. I have 6 tool holder and two are wrong. I remember buying an extra two after getting the initial tool post

I have a Dickson tool post that came with a Clausing Metosa 13" lathe. I never used it due the price and availability of tool holders in the US. The Dickson style requires that the c-c distance on the V mating surfaces be held to a very small tolerance or the holders will not maintain alignment. One can hardly expect that of Asian made toolposts and holders from assorted vendors.

If you have a Dickson style toolpost and holders from the same Asian manufacturer they will probably all work together as they should. The problem comes when you need additional toolholders and retailer has changed his source for those items.

If you purchased a European made toolpost I would expect holders from a different European vendor would fit quite nicely.

I have been using an Aloris toolpost and Aloris style tool holders from a number of sources. The Aloris style holders do not require a high degree of precision in their manufacture to maintain accurate alignment on the toolpost. I have tool holders from a number of Asian and US vendors and they all fit nicely.

The yellow marked problem won't be an easy fix.

I think for now use the good holders, new parting blade and insert to get your mate's job done then decide which way to go eg complete new post set or a couple of holders to replace the dodgy ones rather than rush into buying another toolpost.

Fixed, machined 0.5mm off the edges where the arrows are the the some on the other edges 90 Deg to the marks, if that makes sense

Edited By petro1head on 14/10/2018 08:40:08

Jason explains it perfectly and John Reese is spot on with his comments, congratulations on solving the problem p1h ! However on the video you posted it not quite clear but it looks to me as though you are parting off some way from the chuck ?? how far away are you ?

It certainly looks to be much further than I would recommend and particularly on smaller machines, you need to be as close as possible to the chuck to maximise rigidity, I would suggest a maximum of 1 inch and better closer!

John

Hi petro1head,

I make my own toolholders. The critical dimensions when making this style of holder are the distance between the vees, depth of the 90 degree vee and its relationship to the underside of the tee slot. It is this relationship that controls how far the locking cam rotates.

Looking at your picture of the parting toolholder the cam hasn't been locking.

So your fix makes perfect sense.

Steve.

Edited By fishy-steve on 14/10/2018 12:10:00

It was 2" as I did not want to mark the material I had machined

Much too far out, better to wrap a piece of paper around your work and re-chuck closer in, paper will protect your work, you loose a modicum of accuracy but for your purpose -- parting off this is immaterial, I find thickish paper or business card type card works well when needed.

Guidelines to follow;

Always part off as close to the chuck as possible.

A 4 jaw is better than a 3 jaw for work holding if possible.

If using a QCTP, move the topslide in the direction of the tailstock, so the actual parting tool is over the cross slide.

Lock everything down that does not need to move.

Edit;

i have made 19 Dickson type tool holders for my Bison toolpost, inc 2 parting off tool holders, all for my Boxford.

They all work, and they all do not move.

Edited By thaiguzzi on 15/10/2018 07:04:29

So right, TG.

Particularly your third point, which does not appear to be followed by PH, as it would appear that the parting-off tool is rather outboard of the cross slide. Not good if one already knows one has problems with parting off, especially when cutting too far away from the chuck (with no support to avoid possible chatter - which then resonates, likely increases in amplitude and causes a dig-in in milliseconds).

I think that some, with less than rigid set-ups, are reluctant to shift it to make parting off easier for themselves. That, or they don’t consider the position of the cutter in the context of maximum rigidity.

I, probably like many others, run most often with the top slide moving parallel to the bed. But if I turn the top slide at right angles to the bed and slide my tool post to the right end of the T slot, I can arrange a cutter to be right above the centre of the cross slide.

Another alternative is that the lathe is not so well designed as to allow such positional choice. The QCTP is one example where rigidity is reduced, compared with the old fashioned lantern type tool holder.

Can you show us what you've done to the toolpost, as I'm not at all sure what the problem was and what was done to fix it?

Edited By blowlamp on 15/10/2018 11:36:16