Tramming a Bridgeport

[Rick_B]

Good afternoon folks - I'm in the process of tramming in my bridgeport and was wondering how accurate this needs to be. Right now I'm within .001" in both directions. It seems that the mechanisms that are involved in moving/clamping the head would not allow much closer alignment than that. is there something I'm missing? In a perfect world the goal would br zero - but what is a reasonable number to stop at?

BTW - I'm using a single dial indicator with the mounting post in a collet, cecking both sides and adjusting for half the difference. Rinse and repeat. Do I keep rinsing

Rick

 

[xalky]

How far out is your indicator from the Center? That makes a difference. The further out it is from the center the more accurate your tramming will be. .001 @1" from center is not that great. This translates to .001 acrooss 2" total. 001 @ 4-5" from center is pretty good. This translates to .001 across 8- 10" total, which is pretty damn good. Get my drift.

 

[Rick_B]

xalky - good point. the inicator is 4" out from the spindle center so it sounds like I am in pretty good shape as is?

Rick

 

[xalky]

Well you can try to grt it better, but if it turns out that you cant, then it is what it is. Sometimes a little tap on the head with a plastic or rubberfaced hammer with the bolts just snugged up a little will get it closer. Then tighten all the bolts evenly. But we're splitten hairs. How good do you need it to be, to be good enough?

 

[Rick_B]

At this stage of my machining evolution I'm thinking .001" is probably better than a lot of other variables that will influence accuracy. I think I'm going to call it good until I can challenge that level of accuracy.

Rick

 

[Jeff in Pa]

xalky - good point. the inicator is 4" out from the spindle center so it sounds like I am in pretty good shape as is?

Rick

Rick,
If you're holding .001 in an 8 inch circle, you're doing fine. Did you have all the way locks snugged up? ( both table locks in the front, the side, the knee and the spindle )

Jeff
( I see you're over here too )

 

[Rick_B]

Jeff - no I didn't have any of the axis locks engaged - is that the corect way to tram?

Rick

 

[Jeff in Pa]

Jeff - no I didn't have any of the axis locks engaged - is that the corect way to tram?

Rick

That's the way I learned. Make them snug so you can still move the table against the resistance. ( against, not locked tight ) You want to simulate how the machine will be milling or drilling.

You'll find out real quick how much of a difference it makes on your machine when you recheck it.

One these indicator holders makes life much easier. As an added bonus, they fit around a boring head or other tooling so you can verify centering too.

 

[scleaf]

Made this out of an old drill bar to help to tram my table. It took me a few hours to get it right the first time as I am new, but after I understood what had to happen it was much easier the second time to get it right. I am holding .0005 from end to end 24" of travel. The digital depth indicator works well. I put it in a 1/4 collet and move my the table around with my controls.

 

[dwdw47]

HI: scleaf How are you mounting that indicator in the mill? and what are you tramming on the table that is 24"? are you checking the Gib movement?
The digital indicator's I have used had only an accuracy of 0.001 and repeat of 0.0005. Try using an indicator with a needle and graduated in 0.0005 graduations, a Starrett last word works well and you can see the needle movements easily. The indicator holder shown a post back by Jeff in PA is very good it shows the movement of the spindle.
The indicating of the table is fixed. Unless you sweep the table surface for squareness or if you are paralleling the back jaw of a table mounted vice.
I hope I was clear on my questions and partial answers.
dwdw47