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- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] tramming my new mill
- Date: Thu, 13 Feb 2014 08:57:36 -0500
http://www.practicalmachinist.com/vb/general/tramming-my-new-mill-280091/
Thread: tramming my new mill
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tramming my new mill
Ok, so after buying the mill, phase converter, wiring, ect. ect. I have no cash left to get a small surface plate to accurately tram the head of my mill on. BUT I do have a 18x24x4 granite surface plate. It's heavy as shit. But it's accurate. Bad idea to set this on the table to tram it on?
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02-12-2014, 07:48 PM #2
- Join Date
- Jul 2011
- Location
- Navasota / Whitehall Texas
- Posts
- 160
Do you think the top of your granite plate is ground perfectly parallel to the bottom of your plate? Mine sure isn't ...
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While some may disagree I don't think you really need to put a dead accurate surface up there to tram a mill head. Unless you plan on working to sub .001 (is the mill really capable of this?) then you can tram in to .0005 on just the table itself. Sure it will bounce if you have nicks, pits, and scars on the table but you can still take an average reading as you sweep the table. I used to just run a fine stone (oiled nicely) across the table to knock down the high spots and wipe it clean. You can use 1-2-3 blocks or a gauge block or even just a freshly ground block for the sweep if you want but if this is a BP (or a knee mill variant) then there's little point to attempting to take a reading (unless you're just curious) to closer than +/- .0005 as the mill won't hold that sort of accuracy reliably. There are many expensive CNC mills that will hold .0005 positional accuracy but if your thread is about tramming the head then I don't think you're asking about positional accuracy. To expect a head that perpendicular to table closer than .0005 is IMO the domain of the jig bore/boring mill (grinders are another matter). If it's a manual mill then it's expected range of accuracy is a couple of .001's for square, parallel, and position so you don't need to set the machine closer than the work-piece calls for or the machine is capable of. I was a toolmaker for over 20 years and did work sub .001 sometimes on a mill but it isn't predictable when you do. If you sweep a 10" circle on the mill and the indicator reads +.001 and -.001 over 10" that's .0002 per inch error. That's pretty good for milling, want closer you grind it. Tramming a head is important but only up to a level of accuracy the machine is capable of reaching. Don't flop a heavy granite surface plate up on your mill table, it's not good for either.
michiganbuck and Marty Comstock like this. -
02-12-2014, 08:44 PM #4
- Join Date
- Jan 2014
- Location
- Berlin,CT.
- Posts
- 7
You need to use an indicator held in the spindle and "sweep" the top of the table. Don't indicate a vise or anything else that you would mount to the table. You might want to make sure that the top of the table is clean and free of burrs. Maybe run a large flat stone over the top of the table first. I have a flat stone that measures 2" X 8" by an inch thick that I use to clean up the tops of my tables. Whatever you do do not turn the spindle on with the indicator mounted to it! Turn the spindle by hand. Make sure your knee lock is locked. I always lock my X and y axis also. The way I was taught in the old days (40 + years ago) the reading on the indicator should be about .0005 higher in the front.
michiganbuck and Mike C. like this. -
If you can find a BIG ball bearing outer race, that makes an excellent tramming device. I used one about 8" in diam when I was having to tram the junk Bport copies everybody kept knocking out of whack at my last job. Very lightly clamp the race to the table and then tram the face. A ball bearing race is extremely parallel, so by lightly clamping it to the table, it will transfer the table surface across the T slot grooves and let you really dial it in without having to pick up the indicator quill every time you cross a t slot.
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While I understand what Achilles Bill is saying, I do not totally agree. In the case that you would use a large fly cutter it would leave a noticeable depression in the center of the work. I may be speaking out of turn on this because I am speaking of maybe a 6 inch wide. You may or may not have to encounter that.
Yet back to AB thoughts.... You usually do not want the "trailing end of the tool" to encounter the part you just machined. I have not run a standard mill in quite some time, I have a CNC mill and the head does not have a "tilt" to it. When I was young and learned on a small manual mill I was taught the same thing. Likewise, in a manual mill you mill conventionally and all works well... You do not do that on a CNC. You climb mill and I can tell you I do bearing bores with an end mill.
In summation, What AB is telling you will work well for you on 2 inch wide parts.. Larger ones you will have a definite, measurable low spot in the middle.
Something to store in your vault of knowledge.
JMTCW
MM -
02-12-2014, 09:02 PM
Diamond
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I did not think I'd say this at any point, but I agree 100% with John. He'd be making chips (and $$$) with your mill while the rest us try to split tenths tramming it.
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Good luck finding a 123 block that wasn't beat to hell in that shop. CNC guy used them as expendables to back up his work and butchered them. Bearing race was too hard to drill. When you already need T slot nuts, studs and clamps for the work, you are not saving any time at all by not using them. 99% of the work I was doing on them was too big for the vise (boring out and bushing pump bearing housings and wear rings in volutes). Of course, once we got the Cincy #3 you just squared the work and didn't have to %^&$% with tramming a flimsy turret mill head. 64yrs old and still within .001 on a 10" circle with the knee locked down.
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02-12-2014, 09:54 PM
Diamond
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02-12-2014, 09:59 PM #11
If your mill table is not flat enough to tram off of you must have pulled it from the titanic.
Let me google that for youMarty Comstock likes this. -
The perfect indicator to use with a tramming bar is the old Starrett 196 with the back plunger and the half-inch-diameter shallow convex button. That won't care about nicks. Also I'd sweep the largest radius you can, in several x-axis positions. And sweep the table directly, you don't need to introduce another layer. And stone it first like Bill said. But as for preloading the head out of square, that's to counteract spring on a drill press. Don't do that on a mill that has both an elevating knee and a quill or the two halves of your Z axis will be out of parallel...baaad juju.
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02-12-2014, 10:13 PM #13
- Join Date
- Jan 2014
- Location
- Berlin,CT.
- Posts
- 7
Mick 1958,what would be causing the measurable low spot in the middle? If it's the 5 tenths higher reading in the front as I remember it you needed the 5 tenths in order to have proper tram. It had something to do with the manufacture of the table. Are there any other old timers that remember this?
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Bill,
I was referring to a large fly cutter, if you do not have the head at "0" the cutter will be canted and cut in an arc. Picture a large disc parallel to the table, now tilt it, it will have a low spot 90 degrees of the "tilt". For lack of better terms.
Mick -
Use the mill's table for your reference point. Anything you stack on top of the table can result in cumulative errors
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02-12-2014, 11:32 PM #16
- Join Date
- Mar 2013
- Location
- Oshkosh, Wis. rauchle@ntd.net
- Posts
- 630
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I bought a precision ground, 3/4" x 10" long bar from McMaster; think I paid around $15 for it. I clamp it in a 3/4 collet, raise the table so that it's almost touching the bar, then slide a good 6" angle next to the bar. With a good light behind, tram the head to the angle... boom, I'm done. Close enough for 99% of what I do.
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I bought a precision ground, 3/4" x 10" long bar from McMaster; think I paid around $15 for it. I clamp it in a 3/4 collet, raise the table so that it's almost touching the bar, then slide a good 6" angle next to the bar. With a good light behind, tram the head to the angle... boom, I'm done. Close enough for 99% of what I do.
kidding,,right?? -
No, I'm not kidding. Go find a 9th grade geometry textbook if you aren't clear on the concept of 90-degree angles.
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02-13-2014, 12:49 AM #20
- [machinist] tramming my new mill, Lawrence London, 02/13/2014
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