Head Tramming question(s)

[mxtras]

When you tram the head, do you typically shoot for perfection, or do you leave a small amount of pitch to compensate for spring, deflection, etc? How much and which direction(s)?

I recall reading that Bridgeport targeted a small amount of forward (I think) tilt during manufacturing and that is the reason for the question.

What are the theories/practices?

Looking for advanced info here, not the basics.

Thanks!

Scott

[DareBee]

Perfection definately, IMO if you are cutting heavily enough on a finish cut to worry about head deflection - you need a bigger machine.
I couldn't possibly imagine a finishing cut with a 1/2" endmill causing any stress/deflection to the head.

[dcook]

25 years of experience says perfection, I agree w/ DareBee 100%

[mxtras]

Thanks for your input!

Scott

[Mcgyver]

anything less than perfection is outside of acceptable tolerances - using a tenths indicator of course. You know its right when you get that nice cross hatch pattern with a big fly cutter.

I don't even want to think about angling the head to compensate for deflection, there are so many variables it would be crazy to do and as others have said not meaningfull or measurable on a finish cut. however the mill head will deflect no matter how light the cut - fly landing on the tailstock affecting the cut and all that

[mxtras]

I just ran across a pretty nice collection of info on performing this task and I thought I would post it up:

http://www.sparro.com/KwikByte8.htm

Scott

[One of Many]

Originally Posted by mxtras I just ran across a pretty nice collection of info on performing this task and I thought I would post it up: http://www.sparro.com/KwikByte8.htm Scott

Ha! I Never heard of a 1st WORD indicator! LOL!

How bout a LAST WORD? And I don't like'm any better than a 1st word if there is one. Too many times the stylus slips or something is screwy. Constantly having to flip the direction lever to reverse the point deflection.

I'll take a Best Test or a Federal indicator any day over a Starrett! Gem is another Last Word copy that IMHO isn't worth the box they ship them in.

I wouldn't trust 3 pointing a tramming. Maybe for mills which have only left/right head tilt, but for BP copies and a knuckle joint, 4 point tram is more reliable.


The troubles I have seen with tramming heads to the tables on old or even hobby mills is that the table is not always true to the way surfaces. Or the way surfaces help tilt the table from severe wear.

If you use the crosshatch pattern as the true indicator of the head trammed to the ways. Traveling in any direction NO steps should be detectible. If there are, then the table has either shifted or the table surface is not parallel to the ways.

If the machine will not maintain tram after an axis is moved. Use a fly cutter with a wider swing so the table does not need moved. While that will help produce a flat surface, it will become another pain when setting up for other operations to keep things aligned where tolerances are critical. These mystery shifts in the machine can get frustrating. Setting up a reference, moving 6 inches away to cut another feature, completing the operation flawlessly....only to find the 6" move ended up at 6.03 at the bottom of the part verses 5.990 at the top of the part, rendering it useless from an anticipated level of perfection.

DC

[Geof]

You aim for perfection. However, when you do not get there and have to face a large surface and make it look okay you use a small diameter bull end mill. The small diameter means the out of trueness of the table is negligible over the diameter of the cutter and the corner radius on the cutter means the multiple passes blend nicely.

[One of Many]

Originally Posted by Geof You aim for perfection. However, when you do not get there and have to face a large surface and make it look okay you use a small diameter bull end mill. The small diameter means the out of trueness of the table is negligible over the diameter of the cutter and the corner radius on the cutter means the multiple passes blend nicely.

Normally the head is adjustable, the table is not....you end up at the mercy of the integrity of the ways in relation to the table IF we rely on the table as the true reference.


For those of us with CNC capability with decent condition machines, this ball nose cutter approach would be reasonable, but manual machine users might not like it too much.

In my experience, it is tough to do decent surface hem stitch consistant manually. That could leave a bad finish on a flat surface due to the nose of the cutter having no real surface speed, let alone good chip removal. Not all bull nose cutters are created equal. On worn mills, this will reproduce the wear in the ways too. Not to mention the step over to attempt a smooth surface will make the job xxx times longer. If that is all that is available, then by all means, make due. ZZZZZZZZzzzzzzZZZZZZzzzzz!

If the head were not quite perfectly perpendicular to the table, a fly cutter moving along the least worn axis, should produce the flattest surface the mill is capable of. Even if you must comp the head around to get it to produce a cross hatch. It may not be quite square(which can be compensated for), but I'd expect it should be closer to flat. Things to look for is if the crosshatch comes and goes, or one side of the cutter digs in while moving over a large surface. Determining the cause could be weight shift, loose gibs, way wear or loose spindle bearings.

With a little ingenuity, anyone can make a bad machine look good.

DC

[StealthDumpKits]

Strange, I always thought if a machinist couldn't tram the head in, they just fly cut the table to match.

[mxtras]

Originally Posted by StealthDumpKits Strange, I always thought if a machinist couldn't tram the head in, they just fly cut the table to match.

Holy crap! Never - NEVER cut a factory surface unless you are completely restoring the machine.



Scott

[WhiteTiger]

Go ahead and cut factory surfaces if they are rough or out of true. This "never touch" is fine if you are talking about high dollar production machines that *should* be true and accurate to begin with, but it gets silly when you start applying it to IH, HF and similar low/mid hobby machines.

I had to clean up a booboo on a dovetail surface of my bench mill before I could ever use it. Bit of scrape to fit on a dovetail and then self lap (no abrasive) for all the ways and the machine was good to go. Had I not been willing to recut that surface the machine would have been just another eternal headache; as it was it became a reliable money maker for many years.


Tiger