Michael G
25th Jan 2016, 07:31 PM
My mill is a horizontal with vertical head so whenever I replace the head after using it in horizontal mode I have to re-tram* as it never goes on in precisely the same place. The mill comes with dowel holes to realign but the problem with them of course is that to get a precision fit they are close tolerance. Taking the head on and off (using the dowels for positioning) would wear the holes so that after a while they would be useless anyway. Also, there is only one so I'm not sure how effective they would be. Inspired by my rotary table, I decided that a good solution would be to install a movable pointer
360663
Further more, to aid line up while angling the head, I'd add a 10 minute vernier scale. That way if I wanted something at 22.5 degrees for example I could. I also find that they help get things aligned much more accurately as errors are apparent from the graduations. Schlesinger states tram should be 0.02mm per 300mm (around 8/10ths per foot)which is 14 seconds of angle, so proper tramming would still be necessary but for jobs like the casting mock ups I did, it would be a great help when doing draft angles for example.
The original mark was an engraved line on the ring opposite the graduated scale (picture shows the low tech version of what I was about to do).
360659
To eliminate parallax error between the two scales the new scale would have to be recessed into this ring. I wasn't 100% sure how I could mill a section of the mill vertical head but eventually I used the mill in horizontal with the head on the rotary table. The ring was 181mm in diameter while the table was 200mm. Anyone see a problem with that?
360661
It was tight and I had to remove one of the locks from the R/T but I got there. I kept telling myself I had one good clamp plus one that I was not going to test that much. The movable scale was 50 thou thick (what the material came off the S/G as) so that was the DOC. The first pic shows the mill at the start of the cut, the second is the same thing from overhead. The cutter was offset half the diameter (so the edge lined up with the centre of the R/T) so I got a straight full depth vertical cut. Around half way through I offset it to the other side so my finishing cut would also be full depth vertical (if I had not done this the ends would have shallow, as explained a few posts later)
360660 360662
I was trying to work out how to engrave the scale with sufficient accuracy but then I realised that my R/T had a vernier scale of it's own to 10 seconds, so 10 minutes was not an issue. I put a curve the right radius on the end of some scrap material and attaching the plate (curved in some dinky rollers I bought many years ago) engraved the graduations in the normal way. The graduating tool was built as a one off device so no great care was taken when initially built but after all this time it still gets used around once a year. One day I'm going to have to paint it or something to scare the rust away...
360664
I debated what numbers I should put on but eventually settled for just zero and the two sixties. The gravograph did a quick job of that.
The plate is attached with Phillips head screws to limit the torque - the threads are M5 and 5 to 7mm deep in cast iron. If it was hex key I would be tempted to over tighten.
360658
So now I can replace the head, re-tram and adjust the sliding plate to ensure that zero is zero and not between two divisions as typically was the case. A worthwhile mod if you have a mill with an inclinable head that does not line up exactly when the head is in tram - or there is the pencil mark on masking tape. :~
Michael
*Yes, yes - I should retram anyway (and I do) but it's part of the story...
Michael
360663
Further more, to aid line up while angling the head, I'd add a 10 minute vernier scale. That way if I wanted something at 22.5 degrees for example I could. I also find that they help get things aligned much more accurately as errors are apparent from the graduations. Schlesinger states tram should be 0.02mm per 300mm (around 8/10ths per foot)which is 14 seconds of angle, so proper tramming would still be necessary but for jobs like the casting mock ups I did, it would be a great help when doing draft angles for example.
The original mark was an engraved line on the ring opposite the graduated scale (picture shows the low tech version of what I was about to do).
360659
To eliminate parallax error between the two scales the new scale would have to be recessed into this ring. I wasn't 100% sure how I could mill a section of the mill vertical head but eventually I used the mill in horizontal with the head on the rotary table. The ring was 181mm in diameter while the table was 200mm. Anyone see a problem with that?
360661
It was tight and I had to remove one of the locks from the R/T but I got there. I kept telling myself I had one good clamp plus one that I was not going to test that much. The movable scale was 50 thou thick (what the material came off the S/G as) so that was the DOC. The first pic shows the mill at the start of the cut, the second is the same thing from overhead. The cutter was offset half the diameter (so the edge lined up with the centre of the R/T) so I got a straight full depth vertical cut. Around half way through I offset it to the other side so my finishing cut would also be full depth vertical (if I had not done this the ends would have shallow, as explained a few posts later)
360660 360662
I was trying to work out how to engrave the scale with sufficient accuracy but then I realised that my R/T had a vernier scale of it's own to 10 seconds, so 10 minutes was not an issue. I put a curve the right radius on the end of some scrap material and attaching the plate (curved in some dinky rollers I bought many years ago) engraved the graduations in the normal way. The graduating tool was built as a one off device so no great care was taken when initially built but after all this time it still gets used around once a year. One day I'm going to have to paint it or something to scare the rust away...
360664
I debated what numbers I should put on but eventually settled for just zero and the two sixties. The gravograph did a quick job of that.
The plate is attached with Phillips head screws to limit the torque - the threads are M5 and 5 to 7mm deep in cast iron. If it was hex key I would be tempted to over tighten.
360658
So now I can replace the head, re-tram and adjust the sliding plate to ensure that zero is zero and not between two divisions as typically was the case. A worthwhile mod if you have a mill with an inclinable head that does not line up exactly when the head is in tram - or there is the pencil mark on masking tape. :~
Michael
*Yes, yes - I should retram anyway (and I do) but it's part of the story...
Michael