Tolerance for horizontal milling arbours

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Tolerance for horizontal milling arbours

This topic has 5 replies, 4 voices, and was last updated 25 August 2017 at 19:55 by Rainbows.

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25 August 2017 at 15:26 #313900
Rainbows
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@rainbows
So I want to make a 27mm arbour for metric milling cutters and a 22mm arbour for involute gear cutters. Plan to get use of a CNC lathe for these though so need an actual tolerance to work to rather than feel but tolerances are one of my larger weak points.

Can anyone recommend what sort of size I should shoot for?
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25 August 2017 at 15:26 #8843
Rainbows
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@rainbows
25 August 2017 at 16:33 #313911
SteveI
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@stevei
Hi,

What dimensions/specs do you need?

According to my (not calibrated) micrometers my:

22mm arbour is Ø21.993mm (measured with mic)

27mm arbour is Ø26.99mm (measured with caliper as I can't find the 1-2" mic)

16mm arbour is 15.993mm (measured with mic) — mic starting to warm up in my hand so most likely this is under size

They are old and I can't be sure of the level of wear from use over the last 60 years.

The spacers are bored ~Ø0.05mm over size. There is play if you try and wiggle them.

The bearing support bush end piece are a "tool makers fit". They slide on nicely but there is no play felt. And of course the retention threads at the end of the arbour and nuts are left hand thread.

Why don't you get the specs on the tooling your buying or measure what you have? I have no cutters for them. (I only have 1" diameter tooling) so can't measure the ID of the cutting tools. Hence they will now go back in to storage.

Steve

Edited By SteveI on 25/08/2017 16:44:53
25 August 2017 at 17:00 #313915
not done it yet
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@notdoneityet
I lathed mine (22mm) but I think I might cut the next one on the machine – well at least to finish it to size.

Not yet tried it for turning but I can't see too much hassle, apart from possibly needing to move the cutting tool, to get enough ''long travel", and hand feeding. Morse taper blanks are cheap enough from ArcEuro.
25 August 2017 at 18:38 #313933
Anonymous
An old copy of Machinery's Handbook lists the tolerance on milling cutter bores as on size to 1 thou over. So I suggest the arbor shoild be on size to a couple of tenths under, or the metric equivalent.

I would expect spacers to be slightly oversize, as you want them to bear on the ends, not be off axis because the bore isn't perpendicular to the ends.

Andrew
25 August 2017 at 19:55 #313939
Rainbows
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@rainbows
After scurrying about shady areas of the internet I found some British Standards documentation.

Arbours should be –0.000 5 in. –0.001 in.

Cutters should be +0.000 75 in. +0.000 25 in.

That gets metricated to

-0.0127mm, -0.0254mm and +0.01905mm, +0.00635mm.

That was the 1953 edition. 1995 gives h6 on arbors and H7 on cutters.

-0.000. -0.013mm for 22mm and 27mm arbours.

Sufficiently close that when over the length of the arbour I will be glad to have a new CNC lathe do it rather than my unleveled Keighley. If I had to thought then I would be very glad that both my lathe and mill use MT3 spindles. Stick the machined taper into the spindle and then machine in situ.

Originally I think the overarm "bearing" was in essence a dead centre poking into the end of the arbour. Since that someone stuck a lump of bronze on with four cap head screws to adjust it into the right position. Tempted to replace the entire assembly. Have the bronze bushing made out then lap some bearing bushes to suit it.
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