Bridgeport problem

A

Arky

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I have Series 1 Bridgeport that is driving me nuts. When you cut a keyway ( 3/4 by 3/8 let's say ) it tapers in depth nearly .060 in 4". My buddy "HSS" and I have been scratching our heads trying to determine what is causing this. The spindle is locked and tight. The knee and table does not have any slack. Crossfeed movement does not occur. Machine is level. End mill is new. The cut along the axis is fine. So what's up with this?
Thanks for any ideas, Arky
 
Arky said:
I have Series 1 Bridgeport that is driving me nuts. When you cut a keyway ( 3/4 by 3/8 let's say ) it tapers in depth nearly .060 in 4". My buddy "HSS" and I have been scratching our heads trying to determine what is causing this. The spindle is locked and tight. The knee and table does not have any slack. Crossfeed movement does not occur. Machine is level. End mill is new. The cut along the axis is fine. So what's up with this?
Thanks for any ideas, Arky
Click to expand...

Hmm, without a picture of your setup this might be difficult to figure out. How are you holding on to the shaft? If it is sitting in a vise, you might want to make sure that the surface you are referencing the shaft to is parallel to the Table. if you can, put an indicator in/on the spindle and run it over the bottom of your vise.
 
Sounds like your end mill is pushing up into the collet. Chinese collets? Measure how far your end mill is sticking out and take a cut to see if it moves.

This is why end mill holders are More gooder :)
 
I was using a large vise to hold this 2 and 3/4" shaft. indicated vise in as well as shaft. Vise was true with machine.The collets came with the mill, not import. It's tapering down into the shaft each time. I had to move my shaft to another mill ( Rambaubi) and it did fine.
 
Something is moving. Either the shaft is slipping in the vice, or the end mill is slipping in the collet, or the spindle lock is not holding...etc. .060 is a lot of movement. Without seeing your setup, it's very difficult to say what could be happening.
 
Arky said:
I have Series 1 Bridgeport that is driving me nuts. When you cut a keyway ( 3/4 by 3/8 let's say ) it tapers in depth nearly .060 in 4". My buddy "HSS" and I have been scratching our heads trying to determine what is causing this. The spindle is locked and tight. The knee and table does not have any slack. Crossfeed movement does not occur. Machine is level. End mill is new. The cut along the axis is fine. So what's up with this?
Thanks for any ideas, Arky
Click to expand...

The cut gets shallower? Are you still at the bottom of the cut when you go back for a second pass?
 
I'm thinking the process of elimination. Its improbable that the table is cocked. I would directly clamp the shaft in the tee slot, that rules out
vise issues, I would bring the quill all the way up and lock, and use the knee, that rules out quill lock issues. Only thing left is the end mill
must be driving its self up in the collet. Maybe put a spacer up in the collet to jam the end mill, so it stays put. Some thing wants to
run a taper. Then I think running an indicator across the shaft is ok, its gotta be something with the end mill. You sure the shaft is true.
My last thought is reverse engineering. Think of what to do if you do want that .060 difference, that means shimming the work .060 right?
I'm just seeing the .060 at the beginning it has to be the end mill drifting up.
 
I put a short piece of 3/4" shafting in the same collet I was using to cut keyway. I made sure drawbolt was tight as before and I couldn't move the shaft up or down with a pry bar under spindle. I do think the end mill holders are the best way to hold mills so I'm going to order a set today. This mill dates back to the 60's but still seems to be a good one. I also noticed keyway was not smooth on the sides as it should have been, but I didn't notice any chatter in machine. If I was cutting from left to right, the cutter wanted to dig in as it were a climb cut problem. If I went the other way, the opposite would happen. I placed an indicator with magnetic against table to check for movement and it didn't show any movement in and out of table while cutting. But none of this points to the problem of the cutter going deeper into the shaft regardless of which way you were cutting. Thanks, guys. Arky
 
keep the same setup. Put the cutter in the collet the same way. Reference the height of the cutter with an indicator on the table. Do your cut. Check the height of the cutter. Did it move in the collet?

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Or, for that matter, a line on the cuter flush with the collet with a Sharpie marker will tell the story.
 
I'm thinking end mill is slipping, I have had that issue on my Bridgeport J1. Either bad r8 or a sub par tolerance on the end mill. But make sure somehow your power feed (quill) is not on.
 
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