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- From: Lawrence London <lfljvenaura@gmail.com>
- To: machinist@lists.ibiblio.org
- Subject: [machinist] More Tramming
- Date: Wed, 19 Feb 2014 18:06:52 -0500
http://www.practicalmachinist.com/vb/general/more-tramming-280130/
Thread: More Tramming
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02-13-2014, 11:43 AM #1
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More Tramming
OK, yet another tramming question. For the things I make, flatness is important. Multiple passes of a small cutter can't leave slightly tilted parallel paths, not even tenths. When I use a fly cutter, a dished surface is a big no no. 1) Does it make sense to put a bar in the vise and make a cut in the X direction, and then tram off that surface? IMO, that surface is now parallel to the travel, which is what I want, not the table or vise surfaces, which may not be perfect. Then do same for Y. 2) I know I can measure this, but it would annoy people if I did, so how good or bad are those Kurt swivel bases under a 6" Kurt vise? In fact, how good are the vises.
What I'm after is a surface that can be quickly lapped to flat, and the regular methods aren't quite good enough. Sure, any surface can be lapped, but I'm lazy. I want it closer to start with. I know a surface grinder would solve all, but the shop ain't got one. -
02-13-2014, 12:04 PM #3
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I think getting dead tram is next to impossible on most mills. For a large circle like tree panning tool even though it may look good it is often not near flat. .0001 or .0002 per inch is much in 4 inches. Scallops with a 2 inch fly or cutter may look worse but may be actually better. Much like What you mention.
We had lapping plates of cast iron with grove lines and with checking them for flatness every once and while, and careful hand held figure 8 and turning could make flat and finish. Using Clover compound. Steel plate should work OK.
http://www.ebay.com/itm/Lapping-Mach...item1e86f02c68
Any plate of iron grooved and then sent to a good Blanchard (or surface grinding) shop for dead flat might make one for lower price.
I once made a power lapping table of a car flywheel that was Blanchard ground and then mounted on a vertical shaft geard to turn at about 200 rpm. -
02-13-2014, 12:05 PM #4
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hold lightly in machined aluminum jaws try and take one pass if this isnt possible cut in one direction only rough it down to .004 above finish then finish cit....cant say more without knowing material/size etc. i consistently get .0005 over 8.00 before lapping.
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02-13-2014, 12:22 PM #5
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The tram has to be to the Table Travel (X and Y).
The larger the indicator circle the better the tram.
If you decide to mill a surface, then check it with the indicator, by having the table travel the distance, and check for no needle movement. Both axes. If you lock the knee don't unlock it, or you wont know where you are. Don't know your mill.
Actually you are headed in the right direction. I'm trying to give you additional info.
Regards,
Stan- -
You can't mill flat
You can't turn flat
You can get close with grinding.
If you want something really, really flat, you need to lap. We do the 2 helium light band stuff all the time. That's flat within 0.0000232" That's so flat and smooth that if a fly tries to land on the part, he skids off and crashes.
JR -
Conventional milling is really not a reliable way of getting accuracy's in the sub thou range. Its were grinding and then lapping really come into there own. yes to a degree you can piss about and fight it and improve things. Then you can go by a cheap grinder and realise just how crappy at flat a milling machine really is. Chasing tenths on a grinder is as easy as chasing tenths of a inch on a milling machine if and only if you have the gear to measure at these levels.
Above all you need to consider just how much surface finish really comes into play at these accuracy levels. -
02-13-2014, 01:37 PM #8
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I think you're telling me what I suspected- the ideal tram is to to the actual travel, not so much to surfaces that may or may not be perfectly aligned to the travel. IOW, the table travel is not the table surface. I'm well aware of the rest of the stuff mentioned in this thread and I thought I was clear- I'm a lazy PITA who wants to lap as little as possible, and that means starting with something as close as I can get it.
Originally Posted by Metalcutter
The tram has to be to the Table Travel (X and Y).
The larger the indicator circle the better the tram.
If you decide to mill a surface, then check it with the indicator, by having the table travel the distance, and check for no needle movement. Both axes. If you lock the knee don't unlock it, or you wont know where you are. Don't know your mill.
Actually you are headed in the right direction. I'm trying to give you additional info.
Regards,
Stan- -
02-13-2014, 01:39 PM #9
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Yep, I've got a small Lapmaster and one can do rather well with good technique. Reminds me, I need to spend some time flattening the plate- the last job on it was a bit nasty. I think it was a boron abrasive and carbide parts. Originally Posted by JRIowa
You can't mill flat
You can't turn flat
You can get close with grinding.
If you want something really, really flat, you need to lap. We do the 2 helium light band stuff all the time. That's flat within 0.0000232" That's so flat and smooth that if a fly tries to land on the part, he skids off and crashes.
JR -
You can get a lot flatter with a shaper or planer, as well. Having blued and hand scraped a Blanchard ground cast iron block versus one skimmed with my shaper, I'll take the shaper any day.
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02-13-2014, 07:29 PM #11
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Not always, once the shaper ram wears it cuts the part in a convex pattern. It gets the part flat, but not perfectly flat. Originally Posted by Mike C.
You can get a lot flatter with a shaper or planer, as well. Having blued and hand scraped a Blanchard ground cast iron block versus one skimmed with my shaper, I'll take the shaper any day. -
No, you tram to the spindle axis. Originally Posted by Conrad Hoffman
I think you're telling me what I suspected- the ideal tram is to to the actual travel, .
Ray -
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02-13-2014, 08:26 PM #14
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I thought that was, "Spindle perpendicular to the table travel." Originally Posted by RayG
No, you tram to the spindle axis.
Ray
I think it's the spindle which has to move, so the spindle is trammed to the table travel.
Regards,
Stan- -
Wrong..... there will be no needle movement when the axis moves whether it's trammed or not... ( unless your ways are at an angle to the top of the table Originally Posted by Metalcutter
The tram has to be to the Table Travel (X and Y).
The larger the indicator circle the better the tram.
If you decide to mill a surface, then check it with the indicator, by having the table travel the distance, and check for no needle movement. Both axes. If you lock the knee don't unlock it, or you wont know where you are. Don't know your mill.
Actually you are headed in the right direction. I'm trying to give you additional info.
Regards,
Stan-
)
The axis of the spindle is what you tram to. ( as already mentioned ) if it's not trammed to the spindle axis the cut will be convex ( I meant concave ) depending on the cutter radius and the amount it's out of tram.
RayLast edited by RayG; 02-13-2014 at 11:54 PM. Reason: concave not convex..
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02-13-2014, 08:37 PM #16
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If you are trying to get your tramming down to tenths and you have a mill with both a knee and a quill, such as a Bridgeport, try setting it up so that you don't have to move the knee after tramming. Also try to minimize the movement of your quill and keep as much of it in the head as possible.
I like your idea of machining a piece of scrap to get find the true line that the axis is moving along. The last time I needed a really good tram, I placed a sine plate on my mill table. I put a tenth indicator on the quill and adjusted the plate to read true when I cranked the axis back and forth. Then I trammed to the sine plate. -
"Not always, once the shaper ram wears it cuts the part in a convex pattern. It gets the part flat, but not perfectly flat."
And a worn out Bridgeport will make a convex, angled surface due to table bending and knee sag. Read my post. I said you will get a lot flatter surface. There will be no cupping due to the circular cutter. A Blanchard also has a circular cutter. When you load a circular cutter, it is GOING to flex to some degree and dip on the cutting side, giving you a low spot in the center. Ask anybody who was at the first Savannah, GA scraping session and they will confirm the Blanchard tiger stripes we all learned to hate when scraping our blocks down. -
Tramming a Bridgeport is one thing. Tramming a Deckel type mill with a universal table is a whole different thing. My mill table has tilt, tilt, swivel and slide in addition to the usual mill X,Y,Z axes. The spindle only has one axis, as compared to the Bridgeport's two. You need to think carefully what you are doing when you set this up - sequence of sweeping the table is important.
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02-14-2014, 06:15 AM #19
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Getting the stress out of your iron is important.
A mill level and bearing equally on all feet, a workpiece clamped or maged down bearing on 3 swiveled points.
Good point about working tram being more important than static tram. -
02-14-2014, 10:35 AM #20
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*Sorry for posting this twice but I made it to go in this OP and put in the other by mistake.
The bearing race is a good idea as would also be anything true flat to get above table slots.,
I am beginning to understand why there is confusion about tramming a mill and getting dead flat machining cut.
*This is for tram, and then fine tuning tram as Conrad was looking for tenths not thousandths.
Tram to the vise would only be good if the vise top was true to the table but even that would not be perfect.
Tram to the table (X and Y) would only be good if the table was true to the bed or ways of the machine.
X-(right and left 180*) First the spindle head should be adjusted tram to the X axis (long travel). A pair of 123 blocks would be OK for X but inadequate for tram the Y axis except to place them at front and back of table for Y.
Y- (in and out 180 *) A swing in circle to the bearing race or simply to some true flat in order to be able to include a indicator swing (rotation) to the tram the Y axis (in and out 180 *). The table top, the bearing race, top of trued vise, flat or round true plate, any OK.
Many mills have adjustment for one axis only so the second tram may need a shim rather that an adjustment.
Now with spindle head Rough-Tram X and Y to a true face or the table (true flat vise, whatever) is made.
Next the true tram could be found if that is required for .000? or so flat..
To accomplish this one should mount a single point fly cutter to the head- inflict a cut along the top face of a part and travel for a distance. - look at cut lines and determine from a half circle cut the direction of head movement needed to tram. An indicator swing to this cut can aid in this final tram or a feeler to measure under non running tool. With looking at the cut direction choose the head (tram) movement to make a full circle cut and make that adjustment to tram.
When a two way circle cut cross hatch is achieved in tool cut lines the machine(spindle head) will be tram and then able to cut a flat surface.
Note:
Being tram to only in the X or long axis could have the spindle head at angle to inflict a concave or convex attitude to the Y axis and so high precision flat machining could not be achieved in X or Y movement.
Reply
Thread: More Tramming
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02-15-2014, 11:50 AM #21
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Thanks everybody! I found something interesting. I've always worried about the vise base and fixed jaw being parallel and square, yet now and again I don't get 90 degree cuts. I happened to check the movable jaw and found it was not vertically square and worse, clamped loose at the top. My guess is sometimes the work wasn't solidly clamped to the fixed jaw near the top. Might also explain some unexpected vibration. In my original post I asked how good one can expect a Kurt (6", new) and rotary base to be. I didn't see any specs on their web site.
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02-18-2014, 02:05 PM #22
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Well, you learn something every day. I RTFM for the Kurt and also took it apart. There are two little (optional) o-rings near the front of the movable jaw. The stated purpose is so when you use parallels, the jaw pulls down by .002" and insures the work is solidly on the parallels.
Makes some sense, but IMO it's overall a bad idea. 1) The jaw doesn't fully pull down and thus is at a small and unknown angle all the time. 2) The 0.002" gap at the front encourages chips and crap to get between the moving surfaces. 3) If the jaw is tightly installed, it will never pull down anyway because it's already in contact with the base. 4) Lifting the movable part at the front increases the wear on the back end- I could already see some scoring from this.
The o-rings are now in a bag, carefully attached to the manual in the file cabinet, where they belong. BTW, everything is dead square now.
(I did later find a several year old thread on this issue here.)Last edited by Conrad Hoffman; 02-18-2014 at 04:12 PM.
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. Originally Posted by Conrad Hoffman
OK, yet another tramming question. For the things I make, flatness is important. Multiple passes of a small cutter can't leave slightly tilted parallel paths, not even tenths. When I use a fly cutter, a dished surface is a big no no. 1) Does it make sense to put a bar in the vise and make a cut in the X direction, and then tram off that surface? IMO, that surface is now parallel to the travel, which is what I want, not the table or vise surfaces, which may not be perfect. Then do same for Y. 2) I know I can measure this, but it would annoy people if I did, so how good or bad are those Kurt swivel bases under a 6" Kurt vise? In fact, how good are the vises.
What I'm after is a surface that can be quickly lapped to flat, and the regular methods aren't quite good enough. Sure, any surface can be lapped, but I'm lazy. I want it closer to start with. I know a surface grinder would solve all, but the shop ain't got one.
1) the movable jaw can be up a bit. we often cut within 0.005" of vise jaw. measure top of fixed jaw to vise bottom and compare movable jaw when loose and tight. there is an adjustment if it is too loose and moves up and down too much. i have seen plenty move 0.010"
.
2) when rough milling the part can bow from clamping pressure and be not flat when unclamped. we loosen vise and let it spring or warp the way it wants and then reclamp lightly preferably with a torque wrench for a light finish cut. i have often seen a milled surface 0.001" thinner in center compared to ends by the vise jaws from the bow that happens from vise clamping pressure.
.
3) a part can easily deflect from cutting pressure and spring back as cutter passes. a dull cutter will leave a slightly higher surface at the cutter edges. we check our milled surfaces to a 0.0003" flatness and lap spec. a cnc machine on the servo screen can also show the Z axis servo going back and forth 0.0003". we often have to wait for it to settle down or move the axis and move back so Z axis servo holds steady.
.
4) these is all in addition to a tram problemConrad Hoffman likes this. -
02-19-2014, 11:22 AM #24
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I've held down the movable jaw with a finger clamp many a time to prevent it from raising under clamping force.
Bearing race? Works good but unless your tram indicator precisely tracks along the width of the race you have to keep shifting it.
I have a beat up 1-2-3 block ground undersize and without a mate. Pretty useless until I belt sanded ramps on one end. Plop it on the table, swing the indicator up the ramp to register the surface, note the reading, move the block etc.
Simple, not bulky. Handier IMO than the 320 (I think) bearing race hanging on the wall covered in dust.
BTW who among you have a cryptic number felt tip marked on the side of the nod knuckle? The number is the multiplier needed to transform a sweep error to a nod correction. One sweep, do the math, and one correction... well... OK, two maybe three iterations instead of a dozen converging-but-never-quite-there moves.
Work it out. The sweep dia is X, the horizontal distance from the nod to the near or far extremes of the sweep is Y, and the vertical distance from nod C/L to table is Z. Work a little trig; a little ratio and proportion and Bada-Bing! a constant you can write on the side of the nod knuckle. This number should be the same for all Bridgeports and dimensional clones for, say, an 8" dia tram sweep. Do it the same way every time (including DTI contact angle) and your constant will be - um - constant.
OTH tilt is gravy.
Ever think about two Geier & Bluhm 4-3080 precision level vials attached to a turret mll head arranged to register tilt and nod? The mill itself doesn't have to be particularly level merely stable. Once the head is trammed in, adjust the vials to register level. Thereafter, you can return frorn compound angles to tram merely by centering the vial bubbles. Note: understand you are not using the level vials to establish anything as level. You are merely using them to return to a pre-set position.
YMMV if yours is a turret mill other than a BP. -
02-19-2014, 11:41 AM #25
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Sounds like a cool YouTube video. Originally Posted by JRIowa
That's so flat and smooth that if a fly tries to land on the part, he skids off and crashes.
JR -
02-19-2014, 04:34 PM #26
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Since we are already discussing tramming and I've just spent a few hours trying to get my Wells-Index 860 trammed "perfectly" I have a question. When tramming a mill, and doing it "right", how much deviation is acceptable?
I used a single point DTI at 0.0005" resolution mounted in an Indicol holder and swept across an EZ-tram Accudyne Corporation | Ez-Puller The Only Bar Puller That Is Self Adjusting. After much swearing and "do overs" I was able to get the X-axis almost "dead nuts on" but the Y-axis is still off by 0.0005".
What I found was that even though I would set it to be dead on, when I went to tighten up the knuckle it would change for what to me was "significant". Even after the knuckle is completely snugged down pushing lightly on the head with my hand in either the X or Y direction would show up on the indicator as much as 0.0015". It would return after pressure is removed but still, is seems that even a fairly stiff (for it's size) machine isn't all that "solid".
So, when do you say it's "good enough"?
Thanks,
-Ron
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[machinist] More Tramming,
Lawrence London, 02/13/2014
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- [machinist] More Tramming, Lawrence London, 02/19/2014
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