Boring on the Lathe

[alfagt]

It is a second time I am trying to bore a drilled hole to size with different size, for ex. 0.5 inch leght to 1.25 and the rest of it to 1 inch to 0.5 dimeter. The problem is that the adjustment that I make will produce to different out of tolerances specially on the smaller one. Any sugesstion?

[Mr. M]

When you comp your boring bar one feature goes out of tolerance? Is the insert on center? You could use a variable to shift just one as well if it is a tight tol. feature

[gcode]

the tip of your boring bar is not on the centerline of the lathe spindle

[crazy^millman]

the tip of your boring bar is not on the centerline of the lathe spindle

Yes I would look here 1st. Also might be fighting deflection and chip build up that could be having an influence on the features. Another thing to consider would be order of operations. Are you taking the drill and drilling the hole to size of the tool 1st? Then working smallest bores to largest or are you going largest to smallest? I liked to use different offsets on my tool if I was doing different features with it. Like so T0202 For drilling then T0222 for a diameter and then if I was doing 6 steps I would do it like so T0223, T0224, T0225, T0226, T0227 just so I could dial my critical features down and know what was going on at each feature and adjust as needed for each feature, verse rolling the dice hoping they all stay to size with one offset. Do you have a good coolant stream and flow to the cutting edge? Is heat in the part coming into the equation?

[Guest MTB Technical Services]

Assuming your cutting edge is on center, If your tolerances are that tight that comp kicks you out of your tolerance band for two features, you should use two different boring bars.

[chris m]

--EDIT--

 

I thought you were going from 1.25 to .500, but upon re-reading your post I was wrong. My comments below lose some validity in this case, but are legitimate in others, so I will leave them.

 

--EDIT--

 

 

Higher RPM cuts bigger and you have a big difference in size; if you are using CSS, the small bore should cut bigger that the large bore. If this is the case, offset your geometry (X.4995 versus X.5000) by the amount your dimensions don't track (I usually fake the geometry on the dimension with more tolerance, but it doesn't really matter) and see if you can get control. If not, double-offset it and call it a day.

 

C