Question about tramming a bridgeport

No @pontiac428 I will do that from now on. With the distance I had the indicol set at I had to move the y axis to measure front and rear. Is that okay? I assume it should be “straightish” across it. If not I can shorten up how far I measure when I redo it.
 
mmcmdl said:
On your Y axis ? Is your table clamped ?
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Yes y axis. The part ends up with a taper high on the fixed jaw and low on the moving jaw. The table was not clamped. I was only taking about 10 to 15 thou cuts in aluminum though. I know locking the table is recommended but I figured it was not required for light cuts?
 
Can you drew a diagram of what you're getting ? Haven't had my coffee yet ! :grin:
 
mmcmdl said:
Can you drew a diagram of what you're getting ? Haven't had my coffee yet ! :grin:
Click to expand...
hopefully that’ ls a little more clear. This is off of the milled piece measurements after milling the top and rotating 180* and milling again so it’s likely a compounded number.
 

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To be clear, the part is set on parallels in the vise and you are milling the top of the part. You are getting a taper in thickness from front to back (along the y axis)? How wide is the stock, what is the diameter of the cutter?

If I'm reading all this correctly, the problem is with the vise. Most likely the part is cocking in the vise as you tighten. Less likely, the bed of the vise is not parallel to the table.
 
MrWhoopee said:
If I'm reading all this correctly, the problem is with the vise. Most likely the part is cocking in the vise as you tighten. Less likely, the bed of the vise is not parallel to the table.

To be clear, the part is set on parallels in the vise and you are milling the top of the part. You are getting a taper in thickness from front to back (along the y axis)? How wide is the stock, what is the diameter of the cutter?
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Yes to all that.

The stock is a scrap of aluminum at about 1.1”. Using a 1/2” 2 flute endmill
 
D.sebens said:
Yes to all that.

The stock is a scrap of aluminum at about 1.1”. Using a 1/2” 2 flute endmill
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Put your indicator on the top surface of the part near the edge closest to you. Watch the indicator as you tighten the vise.
 
MrWhoopee said:
Put your indicator on the top surface of the part near the edge closest to you. Watch the indicator as you tighten the vise.
Click to expand...
Also, when you mill your next test piece, indicate the surface along the y-axis after you mill it to see if it indicates that it's flat.
When you remove the piece (or before you install it) indicate along the y-axis of one of the vise ways. If that shows a slope the taper is likely in your vise (assuming the table was trammed and remains in tram).
If your vise has no taper, and the part has no discernible taper before you remove it, it's either a problem seating or holding the part, or your vise jaws. Putting a ball bearing or a block of wood between the part and the moving jaw of the vise will better allow the part to seat firmly against the fixed jaw, which is your desired reference.
If you tightened your knee gib when tramming, tighten it for your cut. If you did not, then don't. Doing so is the better practice. I can't imagine this being the cause of so much taper, but it's worth noting.

GsT

Edit: clarity
 
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