Minnie 1″

[JasonBModerator @jasonb]

The G in the code indicates the tolerance the inserts are made to which results in a sharper egge and that is usually ground & polished rather than just moulded like the M ones. If you looked at them under a microscope then they would have a much crisper edge though they are a little more delicate.

APT sell reaasonable quality ones in packs of two rather than full boxes so ideal to try them out. I tend to use 0.2mm tip radius for the smaller work I do and that would be fine for the Minnie

[james huxstepParticipant @jameshuxstep40895]

Ok guys, just a general question advice post.

During my ongoing experience of making my minnie 1", i find i have to half machine a component with a central bore, make a simple mandrel to fit said bore, turn the component round and finish machine.

Simple enough. Or so i keep thinking.

Say i drill and ream a hole 5/16", and then want to make up a mandrel for it to sit on, what sort of interference fit am i after? if i dont want it to be too loose or too stiff that it gets stuck or have to use locktite.

Im currently using carbide tip to get close then emery tape. With mixed results. Ive heard somewhere that you can creep up on measurements much easier with a sharp hss tool rather than carbide.

[james huxstepParticipant @jameshuxstep40895]

Ok guys, just a general question advice post.

During my ongoing experience of making my minnie 1", i find i have to half machine a component with a central bore, make a simple mandrel to fit said bore, turn the component round and finish machine.

Simple enough. Or so i keep thinking.

Say i drill and ream a hole 5/16", and then want to make up a mandrel for it to sit on, what sort of interference fit am i after? if i dont want it to be too loose or too stiff that it gets stuck or have to use locktite.

Im currently using carbide tip to get close then emery tape. With mixed results. Ive heard somewhere that you can creep up on measurements much easier with a sharp hss tool rather than carbide.

[Clive Brown 1Participant @clivebrown1]

I don't think that there's a hard and fast rule. On the sizes you're quoting then, say, 1/4 to 1/2 a thou" would be OK. I wouldn't use an MT insert for this work, but not much to choose between a GT insert and HSS .

A very fine flat file can be useful for final sizing, (Cries of horror from the experts! ). These files don't seem easily found these days. Try to make a short  lead-in and a  veryslight taper on the mandrel to start the workpiece pushing on.

Edited By Clive Brown 1 on 28/01/2022 08:42:40

[JasonBModerator @jasonb]

The **GT will creep up as well as a sharp HSS tool, you should not really have to resort to emery

One way to do it without the need for loctite is to first set your topslide to a very shallow angle not more than one degree. Turn down a length a little longer than the part you want to hold a couple of thou over diameter.

Then using the part to gauge the size turn down 2/3rds of the length to a shake push fit in the hole using the auto feed on the carriage. You don't actually need to measure this just feel the fit of the two parts

Once you have a good fit use the topslide to turn the remaining third without moving the cross slide.

This will give you a parallel section that lines up the part and the last third being tapered and getting wider will allow you to ring the part onto the taper which will hold it. The arbor will look like an R8 taper but much shallower.

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