Milling Machine Trammel

Bother, JasonB beat me to it. The Pilkington spec on thickness isn't that good either, ±0.13mm I think for 10mm sheet. I rarely tram my mill; when I do a check I use a DTI and four parallels. And before anyone asks the parallels were made by the late father of a friend of mine, who was a tool maker. I can't detect any variation in thickness across all four, using a micrometer. So probably within a tenth or so.

Andrew

You guys are making a simple task complicated. Start with a clear milling table and stone off any high spots, centralise the spindle approx. middle of table.

Set up a simple ‘L’ bar & DTI, swing the spindle until the bar is in the full left position. Place some sort of ground part [vee block, slip gauge, parallel etc.] between DTI and table, raise table to zero DTI.

Swing DTI through 180 degrees and slide ground part gently under DTI, adjust vertical head angle if necessary.

Repeat until both DTI readings are zero/zero or what you judge is good enough.

Tony

You don't even need a DTI. I was taught to use a "z" bar and two fag papers to check the mill head for vertical, but that's another story.

Thanks John !

Now why didn't think of that !

Now i can clean off my magnetic welding clamps as well!

Back to the OP

The magnet wont move around when you rotate the tram head and it also draws the steel nib down onto it ensuring accuracy.

Ian

My point about float glass is YOU CAN CHECK IT! My lump is 9 x 12, a nice size to go on the mill table, when you rotate it around the axis of the spindle keeping the tram indicator still, you can hardly see the needle flicker. The thickness tolerance may be .13 mm but that will be all over thanks to Dr Einstein and the thickness doesn't affect the flatness. It may not be completely accurate, but I can determine its accuracy, and it was a sight better than Mr Myford managed when he set up my mill in his factory

The problem with trammels, or anything else that fits in the chuck, is that they are limited in accuracy by the chuck. And my drill chucks can easily be a couple of thou out (try bunging a 6 inch silver steel bar in it and see what the run out is at the end) and different every time it's re-chucked.

No, I'm an old fashioned bloke - I use a nice chunky bar to hold the dial gauge and proceed just like Tony, but without even the ground flat, just take the reading straight from the bed. If the dial gauge is rigidly held, the plunger can easily be lifted off the bed then rotated by twisting the chuck without changing the setting.

But I did see that the toolmakers at our works use trammels and I suppose they should know, although it may just be to avoid the aching neck ......

Will

I'll be a bit controversial here.

The single gauge will always be spot on, but it is tedious.

The dual gauge systems take a lot of effort to make, and and allow rapid setting, but there are two possible sources of error - first it can be no more accurate than the accuracy you make it with, second, it can be no more accurate than the chuck that holds it, and even collets aren't perfect with 4-6" of overhang.

If , instead, the dials gauges are set using KWIL's /Eccentric's method of setting at a single point then they ought to be virtually as accurate as a single gauge. But, to be honest, as long as the contact patches are within a few mm of each other a set it when you use it trammel like this could be made of a couple of bits of wood nailed together and work just as well.

I have an idea that a pivoting trammel with a pair of fixed probes and a single dial gauge to show if it is off horizontal, might work quite well.

Neil

If I had access to a large lathe I'd get and old disc brake rotor (or something similar) and turn a nice smooth face on it and sized to my mill, firmly weld a nice chunky spigot on it and then return it to the lathe to turn the spigot true as in Johns post earlier. Once made it's mounted in the biggest collet you have and the Mill head is loosened. The knee is then raised until the "tool" is flat on the table without any movement. Head secured, job done.

Another option is part of a nice large universal joint from something like a van. It should be quite accurate to start with but you'll need to turn a nice stub on it anyway to fit your collet. I gave up looking for one but I think VW vans might have something suitable. Guess it might need softening before it can be turned?

I should add that after I thought of this some years ago a search on google provided a link to a company that actually makes small versions of this for modest mills like the X2. Do a google, I didn't bookmark the link. Let's call this "tool" a "Bell Trammel" for want of another name! Only a thought...

Sorry, but that is geometrically incorrect. If you spin, for example, a plano convex lens on the axis of the spindle you will get the same answer from the DTI, but the lens is neither flat nor parallel.

Andrew

Of course if all else fails, you do it the old fashioned way, use a new cutter and watch how it cuts!

The procedure for setting up a dual clock tramming device is to zero both clocks on a common point, the accuracy of the collett or chuck becomes irrelevant unless clock tips really are miles out from a common point.

Mike

I know this will not help much but where did the phrase "out of tram" come from, surely the head or spindle is out of alignment or not square or not true?

Chris Gunn

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Quiote so, Chris

The phrase comes from the process of "trammelling" ... which is [I suppose] a descriptive term for using a trammel.

MichaelG.

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Edit: Corrected typos and added link.

Edited By Michael Gilligan on 19/11/2014 15:22:16

Michael, when I was working, if I was trammelling, I was drawing a big circle.

Chris Gunn

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... which is exactly what these guys are doing; but with a DTI [or two] not a pencil.

MichaelG.

It seems there is a lot of head realignment going on out there, probably due to the design of the Chinese vertical millers on the market. I recall that when I was doing my apprentiship using a variety of vertical millers, most of these had a vertical head that bolted to the machine column. The turret head as we know it now had not been invented then. The head could only be misaligned in one plane provided it was assembled nice and clean, but to align the head in the vertical position, a taper pin was provided to press into a reamed tapered hole drilled through the bolting flange into the machine column. The head would be fitted, the bolts nipped up, and the pin tapped in before finally tightening the binding screws. This would align the head perfectly in 30 seconds. The taper pin was threaded and a nut and washer fitted so it could be extracted when the head was moved or removed. It is possible that other holes were provided 90 degrees either side of vertical.

I do not have access to one of these millers so can only suggest that if there is space for a taper pin somewhere in the head mounting flange(s), the head should be properly aligned using the device of your choice, then it would not be a big job to drill and ream a standard tapered hole with a 1 in 50 taper reamer, and fit a threaded taper pin to ensure repeatable alignment without the use of any head realigning tool. If the head swivels in 2 planes, 2 pins could be installed. I was able to find a source of ready made threaded metric taper pins made for this purpose, but not imperial ones. I would have thought that this would make a good project for MEW.

Chris Gunn

A learners question If I may?

Is it the recommendation to tram the head absolutely flat?

I seem to recollect reading that there might be advantage in setting it a gnat's whisker one way or the other.

If so, which way and why?

John

Hi John

Yes you are right, tilting the head a gnats ensures that the cutter cuts on the leading edge only so that the trailing edge doesn't touch and spoil the surface finish.

I do sometimes do this but most of the time I keep the head square because setting work up setting up, for example with an edge finder is then not accurate and drilling holes, especially deep ones can be a problem.

cheers Will

In the real world just try and get the head as square [trammed] to the table as you can. You will still find that sometimes the tool will cut more on the front or back stroke even then.

Tony

If you tilt the head as you suggest then the gap between the trailing edge and the material will increase as the cutter diameter increases. Also you will only be able to take a cut in one direction only. .