# Tramming a Bridgeport



## Rick_B (Dec 28, 2012)

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


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## xalky (Dec 28, 2012)

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.


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## Rick_B (Dec 28, 2012)

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


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## xalky (Dec 28, 2012)

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?


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## Rick_B (Dec 28, 2012)

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


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## Jeff in Pa (Dec 28, 2012)

Rick_B said:


> 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  )


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## Rick_B (Dec 28, 2012)

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

Rick


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## Jeff in Pa (Dec 28, 2012)

Rick_B said:


> 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.


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## scleaf (Jan 2, 2013)

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.


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## dwdw47 (Jan 14, 2013)

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


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## scleaf (Jan 15, 2013)

dwdw47 said:


> 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



I am mounting the indicator in the spindle (picture has a bolt, but the actual tool has a shaft) and sweeping the table the distance of travel. Since I am new to this I found it to work well and though the digital indicator may not be an expensive one it seems to work ok for my learning projects. I got the idea after watching this video http://www.youtube.com/watch?v=JfANyiS8Hs4


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## Kevin45 (Jan 28, 2013)

When tramming the head, I always drop the table down and extend the quill down as far as it will go. After doing that and bringing the table up to the indicator, I then lock the knee and proceed to tram each axis in. Also you want to have the bolts a little snug when tramming and not completely loose. If you tram with the bolts completely loose, the head is either tipped front to back or tipped side to side. You want the bolts as snug as possible but not too tight where you can't rotate the head. Then once the axis is tuned in, tighten each bolt in a staggered pattern.

BTW...if you have it within .001, you aren't going to get much better than that, unless you keep tramming each axis all day long.

If possible, and you have access to a wet grinder, make a tramming plate. I always kept one in my bench drawer that was 12" square and 3/4" thick. If the vise happened to be off the table, I would set the plate directly on the table and tram the mill. A solid plate eliminates the error of jumping across the slots in the table. If the vise was on the table, I would set the tramming plate on a set of Gage Blocks set on the vise vise ways, but not tightened up. That way the mill is trammed to where your parallels are going to be setting.


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