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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
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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).
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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?

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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)
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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...

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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.
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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

Steamwhisperer
25th Jan 2016, 08:36 PM
The word 'can't' just isn't in your vocabulary is it.
Beautifully done as well

Phil

Pete F
25th Jan 2016, 11:06 PM
Nice one Michael. I don't need them on the Aciera as it uses a different system, but on the little Hercus I found the alignment dowels handy. They would be worthwhile installing, although they do make fitting the head a bit more fussy. Since dowels like that a hardened, wear really isn't an issue. I agree however, one would be pointless and if I were retro-fitting them I'd want them widely spaced, notwithstanding how close the fit is anyway.

However the purpose of the post is to say "Gravograph"????

Michael G
26th Jan 2016, 07:59 AM
I was not concerned so much with the dowels wearing as the holes they go into getting flogged out. Off hand I reckon I would have the head off at least once per month. Apart from the extra fiddling, something is bound to wear sooner or later (even if it is my patience)

A gravograph is a brand of engraver, and the one I have is a IM3. I think a couple of people here have them but useful for neat text and even graphics. They reduce the text from the master between 2 and 7 times, and a variety of fonts are available so versatile. This is mine, imported from Taswegian with the help of PDW. Second photo is a clean shiny one from the web, giving a bit better view of the drive.
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You are not constrained by the fonts available commercially either. In this thread http://metalworkforums.com/f65/t176211-thread-font-dividing-head
I recreated a font from a bit of equipment to see how difficult it was to do. Not very.
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Michael

BaronJ
26th Jan 2016, 09:04 AM
Hello Michael,

Very nice work. I keep toying with making something to help me tram my mill head more easily, but I'm not quite as confident as you.

In your OP, you said



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 (Because of the relief angle in the middle of a milling cutter if I had not done this the ends would have been shallow)


Could you explain your comment please. I don't understand how the ends of the cut could be shallow.
Thanks.

Michael G
26th Jan 2016, 09:35 AM
Best illustrated with a diagram showing what the target shape was and how the cutter sits-
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The top pair of figures show a cutter sitting on the axis of rotation. As you can see from the enlargement at the left, when the cutter is at the end of cut, there is a slight gap between the end of the cutter and the target profile - in this case around 0.22mm (8 thou). This would cause the plate to ride up at the ends of travel - although not a major problem. The end of the cut would not be square to the tangent either. It could be fixed with a file but it's easier to prevent in the first place.

The bottom set of figures shows the same thing with the offset. No problems as the DOC is uniform and the end of cut is square to the tangent.

In both these illustrations all I did was rotate the target profile.

Michael

Pete F
26th Jan 2016, 10:49 AM
What's something like that worth Michael?

I have a small CNC engraving project slated, something along the same size as my 3D printer, just with enough rigidity to run a spindle instead of a hot end. Not a particularly difficult project, but my TUDOO list isn't getting any smaller either. It would be interesting to hear more about those engravers (in a separate thread if required)

Michael G
26th Jan 2016, 09:38 PM
The word 'can't' just isn't in your vocabulary is it?

I've been trying all day to think of a suitable response to this comment but I must admit I can't.

Seriously, I post things on the forum in the hope that they will inspire others and/ or give them insights on how they could tackle things they want to do. I don't see anything I do as impossible or for that matter highly difficult. The difference is perhaps that being (mainly) self taught I spend a lot of time thinking about how to do things. I do like it when people ask questions because who knows - there could be a better or simpler solution* out there that I've missed.

I must say that this forum can be very thought provoking at times - some of the problems that you guys toss up I'm just itching to get stuck into, to find out how something works or even if an idea I've seen or had will work. At the moment I'm thinking about how to drill curved holes, make push broaches, devise a mechanism to engage/ disengage a cone clutch while rotating on a shaft and a few others.

Michael

*Engineers talk in revered terms about the 'elegant solution' - a solution to an issue or problem that is inspirationally simple and efficient - although conforming to the duck principle a lot of work may have gone into getting to that state.

BaronJ
27th Jan 2016, 01:17 AM
Thank you Michael,

Your drawing explained the issue perfectly. Now I understand the effect and the cause. I admit I was never very good with geometry.

PDW
27th Jan 2016, 01:51 PM
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.

Use stainless button head cap screws. The hex recess is dead shallow and they round out long before they strip threads, leaving you with an interesting exercise in getting them out again - especially if you used Loctite when installing them. Guess how I know that....

PDW

PDW
27th Jan 2016, 01:54 PM
devise a mechanism to engage/ disengage a cone clutch while rotating on a shaft and a few others.


I did that 30+ years ago when I designed/built a lathe apron from a start point of a leadscrew with one bevel gear on it. IIRC I used a thrust bearing and paired push pins operated by a rotating cam. Sold the lathe so the fine details are gone. I do know I cut the angle a bit fine as it had a tendency to stick and needed a bump to get it to release.

PDW

Vernonv
27th Jan 2016, 02:08 PM
Use stainless button head cap screws. The hex recess is dead shallow and they round out long before they strip threads, leaving you with an interesting exercise in getting them out again ...Angle grinder or dremel with a thin cut off blade and cut a slot in the head. Then use a flat bladed screw driver to remove the screw.