co-axial indicators

[Tony Pratt 1Participant @tonypratt1]

I cannot understand why people don't just tram the table but have to introduce gadgets into the equation.

Tony

[Jon LawesParticipant @jonlawes51698]

Would tramming the table help in this case? My understanding is that this is something else entirely?

[Peter Jones 20Participant @peterjones20]

You tram mill head not table. Co-ax indicator just makes it easier

[Oily RagParticipant @oilyrag]

I have a nice compact indicator which has a rack and pinion adjustment for diameter giving about 2" of travel, the crucial part of any indicator is the dti you use with it, for picking up a bore or spigot to 'spot on' I use a Mercer dti with 0.0001" scale markings with a range of +/- 0.008" – for more general 'close enough' I use a dti with major scale of 0.001" with subdivisions at 1/2 a thou but with a much bigger range. I get 'spot ons' to 0.0001" TIR and 'close enoughs' to 0.001" TIR. Total loss of headroom is probably just over 2" when held in W20 collet – more if used in a W20 to ER25 collet chuck.

For picking up edges I use a wobbler, or the cutter and fag paper, for centre popped holes after being marked out and scribed, then 'popped' with an optical punch I use a Zeiss centering scope. The later is just so good I can set a pair of holes to better than 2 tenths.

[IanTParticipant @iant]

One of these has been on my TUIT list for a very long time….not sure it's ever going to make it though…

Zero-IT

Regards,

IanT

[old martParticipant @oldmart]

I had never thought of tramming a mill head using a co axial indicator. I would have thought that a ground flat precision plate would be needed on the mill bed because of the tee slots.

Using a lever type dti with a mirror is one of the principal reasons for having a co axial indicator.

Edited By old mart on 12/12/2020 17:52:54

[Clive FosterParticipant @clivefoster55965]

old mart

Easiest way to use a co-axial indicator to tram a mill head to the table is to just rotate by 180° by hand to compare side to side or front to back errors. Just lift the probe over the Tee slots. I use the long bent probe on mine.

Ultimately not as accurate as the two indicator or one indicator on an arm (zero-it) type but mine does well enough.

I've never got round to actually measuring the accuracy but in practice the error on my Bridgeport seems to be something under a thou over 15" (approx).

Truth to tell using the co-axial indicator was a quick, temporary expedient until I got something better made up. That might have been 15 years ago! Nowt so permanent as a temporary job.

Clive

[Iain DownsParticipant @iaindowns78295]

IanT – that looks an interesting design, but I think it's overkill for tramming.

Here's what I made

It's a 16mm bar with a 10mm hole cross drilled in and a set screw in the bottom. The indicator on the end is a micron indicator I won from ebay a while back, but it's easy enough to mount any indicator on it.

The trick with tramming is that the operation is entirely symmetrical, so whist there may be droop due to poor rigidity, it will be the same on both sides.

I used this today to re-tram my mill which had gone well out of tram (by 2mm over 330!) probably because I hadn't properly tightened the head last time and some dig-ins due to an odd material. I appear to have improved that to 7 microns over the same distance which is better than I expected. the majority of that was due to tightening up the head bolts!

Iain

[Clive FosterParticipant @clivefoster55965]

Iain

Simple and effective. Nice job.

Pretty much the sort of thing I was going to make to tram my Bridgeport head based on an essentially the same design I found somewhere. Then I thought "Hang on, I've got that co-axial indicator. If i point the long bent probe out sideways it will do pretty much the same thing!".

The rest is history but a co-axial is floppier and inherently less accurate.

Clive

[Oily RagParticipant @oilyrag]

Below are photo's of the Hole/spigot centre finder I mention in a previous post. I can't remember where this came from but suspect that I bought it in the States during a visit whilst working there about 20 odd years ago. I thought it was a dinky little piece of kit and has proven to be accurate, easy to use and robust.

Here is the Mercer 1/10th division large dial dti I generally use with it

And for tramming I use an 'IndiCol' clamp which goes on the vertical quill. This Is used in conjunction with a large diameter (about 10" or so) outer bearing ring laid on the table to get over the Tee slots. On my mill the table, which can be swivelled and tilted, or just tilted for the standard table, has a taper dowel for setting to zero. Likewise the head which also swivels is also fitted with a taper pin to locate zero, This makes re-setting a straight forward procedure. I do occasionally check after moving either but there has never been any inaccuracy as far as I can witness with the kit I use here. Here is the IndiCol:-

[Author]

Posts