Tramming mills

[old mart]

Last Saturday, Mike and I spent some time tramming the Tom Senior light vertical at the museum. It was slow and fiddly as we spent more time going the wrong way, and then the clamping up caused some slight movement. It is close, but not perfect.
What would be a reasonable tolerance, bearing in mind that the maximum size of shell mill used on it is likely to be no more than 80mm, 3 1/8"?

[A.K. Boomer]

It seriously all depends on what type of work your going to be doing... how precision do you need it to be? Your tram needs to be better then the needs of the work your creating...

[loose nut]

Mine is within a half thou. Getting closer could drive you nuts, me definitely so I'm happy.

[Stu]

Mine is within a half thou. Getting closer could drive you nuts, me definitely so I'm happy.

Half a thou over what length? I go out about 5" from the spindle.

[Doozer]

When using a fly cutter or shell mill, sometimes you want to tip the head on purpuse
so you don't get the double cut from the drag.
Bottom line is, it depends.
Tramming a Bridgeport type mill should take 5 minutes.
Everyone here gets so jacked up about tramming.
Not sure why.
And everyone thinks they need a brake rotor or something.
I once had a machinist job doing secondary ops for the cnc department.
Mostly drilling weird angle holes on parts that came off the cnc.
Really expensive parts.
They had to be sine bar accurate angles.
I tipped the Bridgeport head 6 times a day.
If you took longer than 5 minutes,
you would be fired. No joke. It was that kind of shop.
(small shop, eastern European owners, son ran the place).
Just practice with an indicator off the table
and LEARN to anticipate how much to move the head
based on one swipe around the table.
That's all I can say. Once you see the correlation, you can
make the correction quite easily.
3 swipes and 3 corrections, and you should be within less than a thou.
Not the moon shot here people.

-Doozer

[A.K. Boomer]

When using a fly cutter or shell mill, sometimes you want to tip the head on purpuse
so you don't get the double cut from the drag.


-Doozer

Ahhh - ok, not sure what kind of parts your making that you want "dished" but whatever works for you,

Iv never tilted the head in fear of getting the double cut and in fact have milled lots of cylinder heads and it's mandatory to see the double cut or somethings wrong, your not really removing any material it's just giving it a cross hatch and you should see BOTH patterns perfectly and one should not dominate, when you see that you can be assured and say to yourself "that's the stuff"... If you are milling a cylinder head it's esp. critical as your cutter has a wide swath, don't see this effect DON'T bolt the head on because it means the bridges that separate the cylinders are LOW and that's exactly where your new head gasket will BLOW out...

[old mart]

On the drill mill which is not adjustable for tram, the double cut is visible one way, but not the other, there must be a tiny bit of tilt.
We had to go home from the museum before trying the Tom Senior tram with a shell mill, I will post the results next Wednesday, and the actual tram figures.

[Doozer]

Ahhh - ok, not sure what kind of parts your making that you want "dished" but whatever works for you,
.

If the surface finish requirement is tighter than the flatness callout, that is how you do it.
Done in Manufacturing all the time. Use the tolerance you are given.

-Doozer

[A.K. Boomer]

A nice radius tool is not going to make the surface any rougher in a crosshatch - it actually will improve it --- no need to ever tilt a head to eliminate the pattern unless it's some kind of strange cosmetics your worried about?

[Tundra Twin Track]

I use a 10" Lathe Chuck ,you can hear it contacting the table sqaure when dropping the Chuck slightly with quill,not scientific but seems to work.

[Bob La Londe]

Depends also on the size and type of cutter you are using. Half thou over 6 inches is reasonably decent. Many people are getting good work done with worse.

[Bob La Londe]

In the Starrett Tools & Rules booklet on page 7 read the second paragraph.

Don't have one? Ask them for one.

[tomato coupe]

Iv never tilted the head in fear of getting the double cut and in fact have milled lots of cylinder heads and it's mandatory to see the double cut or somethings wrong, your not really removing any material it's just giving it a cross hatch and you should see BOTH patterns perfectly and one should not dominate, when you see that you can be assured and say to yourself "that's the stuff"...

The problem is, one pattern is from cutting and the other is from rubbing. Rubbing is bad for several reasons.

If you are milling a cylinder head it's esp. critical as your cutter has a wide swath, don't see this effect DON'T bolt the head on because it means the bridges that separate the cylinders are LOW and that's exactly where your new head gasket will BLOW out...

Tilting the head to give you .0005" clearance on the backside prevents rubbing and only leads to .00025" of concavity. Does a head gasket require better flatness than that?

[Mr Fixit]

Hey TTT,

How are you using the chuck? Is it secured in the quill and you look for flat contact on the bottom of the chuck to the table? Or is it another method?
Curious minds need to know.

TX
Mr fixit for the family
Chris

[A.K. Boomer]

The problem is, one pattern is from cutting and the other is from rubbing. Rubbing is bad for several reasons.

if your cutters sharp but with a radius it will actually still remove the highs of the adjacent pattern while also leaving the first pattern just as visible --- id say it's more than just rubbing if you have proof of the finer particulates staring back at you after the last cut... it passes the fingernail test better also - is smoother in all directions

Tilting the head to give you .0005" clearance on the backside prevents rubbing and only leads to .00025" of concavity. Does a head gasket require better flatness than that?

What swath measurement are you going by? tilting the head .0005" on the backside and coming up with it leading to only .00025" is an absolutely pointless erroneous measurement without including the cutting swath...

and irregardless - if the surface finish is better with crosshatch and the part is less dished then why in the world would you even risk it? I work on mostly aluminum heads AND blocks - with almost all head gasket replacements the blocks you mostly leave in the car unless absolute needed that you have to pull them, lots of head gaskets have to be replaced cuz the pooch has already been screwed, so you can expect at least a mild overheat, heads take the brunt of it but aluminum is a squirrely material when it comes to overheats, it's a compound error thing, the closer you get the head to perfect the better so even to your misguided value of .00025" the answer is yes - if the block is already pushing .00175" out then the addition of just .00025" could push the grand total into the red zone (off the top of my head certain subaru specs)

this is not yesteryears engines with spongy forgiving head gaskets, these are three piece steel with a thin sealing membrane on each side,,, not a whole lot of room for error --- yet out of hundred's iv never lost one, and for good reason...