Need sage advise of truing up Bridgeport style vertical mill.

[toadboy65]

The mill I have is a bridgeport clone from Taiwan, from when they seemed to be making pretty good machines. My problem, when I use the head to make cuts with complex angles. then have to return to return the unit back to square with the table. Today, I noticed it seemed a bit odd, so I indicated it the way I normally do. I run the spindle down all the way, and indicate off of that while raising and lowering the table. It takes a lot of time and effort, and at best I am close, with a couple of ten thousanths variation.
If I want to set up for precise work, A can spend an hour or so, most of which is cranking the table up and down, and making tiny changes to my adjustment bolts.
Yes, I could go out and buy a better mill. Unless someone wants to trade, that is unlikely.

I bet others have found tricks or shortcuts to get the head back to true on both axes. As it is, I only yaw or pitch the head when I really need to, as resetting is such a chore.

Thanks- T

 

[danallen]

The mill I have is a bridgeport clone from Taiwan, from when they seemed to be making pretty good machines. My problem, when I use the head to make cuts with complex angles. then have to return to return the unit back to square with the table. Today, I noticed it seemed a bit odd, so I indicated it the way I normally do. I run the spindle down all the way, and indicate off of that while raising and lowering the table. It takes a lot of time and effort, and at best I am close, with a couple of ten thousanths variation.
If I want to set up for precise work, A can spend an hour or so, most of which is cranking the table up and down, and making tiny changes to my adjustment bolts.
Yes, I could go out and buy a better mill. Unless someone wants to trade, that is unlikely.

I bet others have found tricks or shortcuts to get the head back to true on both axes. As it is, I only yaw or pitch the head when I really need to, as resetting is such a chore.

Thanks- T

Even with a true Bridgeport tramming the head is a chore especially if you moved it both ways. There are no short cuts or easy tricks.

 

[MRA]

I second that - it is a pain. I do it with a dial gauge in the chuck on an L shaped bracket, so the dial gauge is an inch or two off-axis. Then you can use it on a bit of flat plate clamped to the bed - or the bed itself I suppose if it is clean enough - to true it up L and R and then front and back. Sometimes I check it with a big face cutter and some scrap plate, to see if I get scallops (L-R) or the 'factory roof' (front-back). That reminds me I have to do it soon on our machine (which is at work) as we performed a head transplant - someone gave us a machine which seemed better than the one we had, but there was something wrong with the CVT so we swapped the heads over.

(Edit - I note you are looking for tenths. I suspect you get a lot closer with your method than I do!).

 

[Chiptosser]

I have never heard of tramming a head by moving the table up and down. Swing the spindle and adjust the head with the table locked.

 

[MADJACK]

I have never heard of tramming a head by moving the table up and down. Swing the spindle and adjust the head with the table locked.

I run the spindle down and check it for even contact with a cylinder square, after I rough it in that way, I use a dial indicator ro measure and sweep left and right, then front and back to fine tune it. I have the indicator about 6-8 inches off center.

Ive been thinking about getting an old brake disk to sweep the indicator on....

 

[Badhippie]

How can you tram the head by moving the table up and down. (You can’t) Also if you’re expecting that type of a milling machine to provide accuracy to .0002 and stay there. Probably not going to happen. Even with a Bridgeport with scrape ways and brand new it’s accuracy is only expected to be around .001-.0005. I have a 10x54 Taiwan mill. ThatI can set at .0002 tram and over the course of a week it would move approx .0005-.0015. I just took it apart last week and found the arm the head bolts to the ways on the side with the gear that allows it to move inward and outward. That side ways are cracked and I believe it is allowing the head and arm to sag somewhat. I just finished welding and brazing the arm up yesterday afternoon. And can tell you from experience that is some of the worst casting I have seen the cast itself is good but the casting is very poor. While I was repairing the casting I also added some extra bracing inside to help stiffen it up some. Also I use an Edge double indicator set up they sell it works very well and makes tramming a mill a lot easier and less of a pain in the butt. This gauge reads down to .0005 and works pretty good and it was pretty reasonable in price. Also don’t move your table up and down to tram your mill find a spot the the column will reach and then lock your table and lock your x&y axis then tram your mill.

 

[davidyat]

I try to keep my head in the same position after tramming. If I need to do anything involving angles, I try to use my adjustable vise clamped to the table and a digital angle cube. Since I'm not doing any rocket science, I can get good results for what I do.
Grasshopper

 

[Gabe J DiMarino]

I do something similar to MADJACK I use a precision square on the mill table and slide it till it comes in contact with an extended quill .Adjust the head till it looks good left to right and front to back .Snug up the bolts . I have a plate that has been flat ground very accurately .I put that on the table put my test indicator in the spindle and sweep the plate . Takes me 10 minutes to get within a few tenths over a 13 inch diameter . Now I have been doing it like this for over 30 years so your mileage may vary .

 

[toadboy65]

I finally got to ask my mentor about this. He said his best method is to lay a granite surface plate on the bed, and indicate in a circle with a collet-mounted horizontal beam. I guess the longer the beam the more accurate, until the weight and flex of the beam overcomes accuracy gained by distance.

The discussion of those techniques tell us how to get it as square as possible, but do not really address the issue that is bothering me, which is how much time I lose setting it square after moving the head to mill at some angle.
What I had been doing after using the head to mill angles is to run the quill down, place a square on the table next to the column, and eyeball it to close to square to begin the process. Prior to my original post. I experimented with indicating the column while moving the table, which turns out to be a less than optimal solution, rather than a shortcut.

The sort of work I am doing,or at least how I am doing it, demands as much accuracy as I can get. In a perfect world, I would have been able to afford machines more suitable to obtaining higher tolerances.
I do like the ability to tilt the head of the mill. It seems to me that in designing a machine with such a capability, there would be a provision to quickly and painlessly return and lock the head to square on both axes.

Certainly it seemed worth the effort to post the question here, before going to the trouble of engineering a solution to my problem, only to learn later that an effective and elegant solution is already out there.

 

[peterl95124]

I try not to ever change the tilt of the head unless absolutely necessary, instead I'll do anything and everything to clamp the part at the needed angle. Because tramming the head is a pain, no matter who made the mill. There is no trick, just takes time and gets better with practice, also I have to tighten the bolts slowly and re-check the alignment frequently as tightening changes alignment.

Also there are many different ways to measure the verticality of the head, the most common is seeing that it is truly perpendicular to the table, the less common is seeing that it is perpendicular to the X-Y axies, the least common is seeing that it is truly parallel to the Z axis. I usually do the second one because I don't trust my cheap import vise, but I'm really looking forward to trying the third some day because I have a nagging worry that raising/lowering the table vs extending/retracting the quill affects X-Y location.

 

[Gabe J DiMarino]

If its that difficult to align your head maybe you should get a tilting table and some sine vises and leave the head alone and tilt the work piece ?

 

[mcostello]

Raising the table will show the difference in tilt or nod in the quill. Put an indicator on the wuill and try it. I use the horizontal beam method as it sweeps a circle as wide as the table or wider if I wish.

 

[toadboy65]

On my table saw, there is a little adjustable stop so that when you tilt the blade assembly, then return it to square, it stops at the right place. How square that is depends on how much work you are willing to put into setting it up initially.
That concept would not translate readily to the mill, as there is a lot more weight and mechanical advantage involved. Also, it rotates both ways.

I see two remaining options:
If you could easily and accurately read the angle of arc, you could just adjust it close to 0°00'00", like you do when you return to origin with a DRO. What my machine came with is a strip riveted to each side of the moving surfaces, with degrees printed on one side. It serves only to get within a degree or so. A degree of error might as well be 1000 miles.
Perhaps a modified scale with a very fine line and a magnifier?
A variation on that might be a holder for an indicator on one side, and a dowel or something attached to the other. Zero the indicator before tilting, then it should be easy to watch the indicator when returning to square.

The other idea would be something like a tapered socket one one side and a tapered pin on the other. You might use the normal adjustment bolt to get the pin within range, then push the pin in for final alignment prior to tightening the locking bolts.

It does seem like a design flaw in the machine. Everything else about it is in thousanths, but the head orientation is "ballpark".

 

[Richard Carlstedt]

Two suggestions..
1. you want speed ? here is the fastest, but not the most accurate...maybe ???
We did this at work ( in the Die shop) on our Bridgeports for fast turnaround of angled milling
We had a round plate 7-8" in Diameter and maybe 3/4" thick with a center spigot 7/8 inch diameter and maybe 1" long . while the head was still tilted,mount a 7/8" collet and the plate in the spindle using the spigot ( which is perfectly parrallel to the plate.
Extend the quill 3-4" ( good support) and then rotate the head approximately to plumb , now raise the table till it touches and adjust so the plate becomes flat on the table ....but here is the secret to speed.....you loosen the clamps on both the head and tilt and use the table to lift slightly the head. sort of want to be in the slop area of the adjusting screw and then tighten all the screws !. Done ..donot raise so hard AS TO tilt the head backwards , just in the sweet zone. ....Periodically , turn on the spindle -slow speed to confirm the plate was not bent ---you will see wobble if so

2.
Most guys make tramming a big deal ..it isn't
You want the quill to be extended and you want a 8" offset on your indicator arm for accurate work
First, (Important ! ) indicate L & R AT THE REAR of your BP Table ..say 1/4' from the rear edge.
Do L & R until matched, Make sure the indicator faces the left side handle when its on the left !
That means you look at it from the far L or R ! now when the readings are equal , you simply
tram to the front edge off the table ( 6 o'clock) and move 90 degrees to the Right side of the table to the 3 o'clock position ..Forget the numbers on the dial ( ! ) , you just want a match reading , as BOTH will change in a tilt , and if the difference is getting smaller, you are adjusting in the right direction. So your first tram is 180 degrees and the second is only 90 degrees and the dial is fully readable at all times - so you only have readings at 9,6, and 3 o'clock !
So no table moving ! No Numbers to remember , you are indicating on the smooth sections of your table. and the dials remain in normal sight . No plates to worry about ,and the 8-16" swing gets you really accurate settings

Rich

 

[L98fiero]

I finally got to ask my mentor about this. He said his best method is to lay a granite surface plate on the bed, and indicate in a circle with a collet-mounted horizontal beam. I guess the longer the beam the more accurate, until the weight and flex of the beam overcomes accuracy gained by distance.

That only works so long as the top and the bottom of the surface plate are parallel but for sure, not all surface plates are made that way, the bottom is not a precision surface, I'd at a minimum, check parallelism be fore tramming like that. A large brake rotor would work as well though, if you don't have a surface plate and would be easier to move and check parallelism.

Personally, I just tram across the width of the table, get the indicator readings within better than 0.0005 and you won't see the difference with a 4 inch fly cutter or face mill.

 

[TimTaylor]

Similar to Rich's #2 with indicator mounted to spindle:
1. move indicator to left side and zero.
2. rotate spindle 180 deg, note reading and adjust left/right angle of head to take out half.
3. re-zero and repeat as needed to get within desired tolerances.
4. rotate spindle/indicator 90 deg to front of table and adjust front/back to get same reading as side to side.

That said, for really high precision, I have two other options available:
1. High precision electronic level and fixture that will let me measure within 0.001 deg
2. Precision laser geometric measurement system that can measure to one micron

 

[mrehmus]

In days gone by, Bridgeport made circular rings (parallels) of about 10-12 inches in diameter so one could mount a dial indicator on the spindle and sweep the circle. I made the equivalent by obtaining a 10-inch outer bearing race and having it ground to within a tenth in flatness and parallelism on both sides. Makes tramming a breeze.
The other trick is to torque the nuts holding the head in place to the factory-recommended torque. On my Bridgeport, that is 45-foot pounds which seems a lot. The head does not go out of tram unless I crash the cutter in a fairly big way.

 

[clockworkcheval]

Leaving the head in a well trammed position is my favorite. As a matter of fact it is often easier and thus more precise to set a relatively light angular vise or sine vise to the required angle than the relatively heavy head.
Some makes have a tapered dowel for the zero position, but beware! This zero postion on my otherwise quite precise Aciera F3 toolroom mill is definitely not in the zero postion! On my WABECO F1210 mill the zero position dowel does sit in the zero position.

 

[roughcaster]

bridgeport state that the table is fitted to be slightly high in front, usually .0005"

 

[ChazzC]

I finally got to ask my mentor about this. He said his best method is to lay a granite surface plate on the bed, and indicate in a circle with a collet-mounted horizontal beam. I guess the longer the beam the more accurate, until the weight and flex of the beam overcomes accuracy gained by distance.

The discussion of those techniques tell us how to get it as square as possible, but do not really address the issue that is bothering me, which is how much time I lose setting it square after moving the head to mill at some angle.
What I had been doing after using the head to mill angles is to run the quill down, place a square on the table next to the column, and eyeball it to close to square to begin the process. Prior to my original post. I experimented with indicating the column while moving the table, which turns out to be a less than optimal solution, rather than a shortcut.

The sort of work I am doing,or at least how I am doing it, demands as much accuracy as I can get. In a perfect world, I would have been able to afford machines more suitable to obtaining higher tolerances.
I do like the ability to tilt the head of the mill. It seems to me that in designing a machine with such a capability, there would be a provision to quickly and painlessly return and lock the head to square on both axes.

Certainly it seemed worth the effort to post the question here, before going to the trouble of engineering a solution to my problem, only to learn later that an effective and elegant solution is already out there.

Moving a large enough granite surface plate around seems awkward; plus, I don't know how parallel the top & bottom of a surface plate are.

I use a Boring Research Spindle Square (similar to the Edge Technologies, but less costly if you buy your own dial indicators Boring Research Spindle Square. The spacing of the indicators can be changed, and the largest separation is 6" C-C rather than the fixed 5" C-C for the Edge. I use a 9", 1/2" x 3/4" parallel so I can use the greatest baseline on my Mini-Mill (table is only 4-5/8" deep and I have a3" vise).