Bridgeport Series 1 - Hole diameter variations

[jim_cliff11]

Hi,

I have a Bridgeport Series 1 2HP mill running Mach3 as a replacement to the old Anilam Crusader. The functionality is unbelievable, and so far the mill has been running Monday to Friday on various jobs. However I've a newly discovered issue:

On spiral drilling or pocketing out a 25mm deep hole (in mild steel) to say 28mm diameter. The bottom half of the hole is out by about 0.30 to 0.40mm, essentially giving me a tapered hole. I'm trying to figure out if this a software or mechanical issue. So far I'm leaning towards the latter. Could the quill bushes be worn inside the headstock? The quill in total is having to extend 50mm down as I have a 25mm clearance due to fixtures. Maximum Z travel distance between limit switches is about 3-4", so 50mm shouldn't be asking to much. Either way, could the increased leverage on the quill at depth cause this issue?

If so how can I go about fixing it?

Is there anything else I should check?

Thanks

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[Jim Dawson]

That sounds mechanical. Is the head in tram? Out of tram might cause that, maybe.

I guess you could extend the quill and see if it deflects relative to the rest of the head.

[CNCMAN172]

Agree this sounds like a TRAM issue. Check it using a precision square and a long straight drill bit or endmill.
Russ

[jim_cliff11]

Ok thanks for the replies.

I think the tram is out, so I'll have to readjust it tomorrow. Found a good tutorial on Youtube!

However, I'm not fully convinced tramming is the cause. The fact the holes have a larger diameter entry side than exit side makes me think there is excessive play in the quill.

I'll try your recommendation Jim and post back with the results.

Thanks

[skywalker4]

spiral drilling? do you mean boring? the only times i have had that issue it has been tooling or feeds and speeds.
I have also heard boring called offset reaming. lol

[jim_cliff11]

spiral drilling? do you mean boring? the only times i have had that issue it has been tooling or feeds and speeds.
I have also heard boring called offset reaming. lol

Either way, it doesn't matter what it's called in this instance. I've tried numerous speeds, feeds, depth per revolutions etc using Gwizard as guidance. All holes bored had the same issue.

[Bdrangdo]

Easiest test to make is to put a clock on the end of the tool and put some hand pressure on it and see how much movement you have, maybe there is some wear in the quill but that can usually be negated by gently clamping it. It is surprising just how much twist you can get in the overarm if it is extended, try bringing the workpeice closer to the pillar. If all else fails do a light finishing cut to minimize deflection.

[Jim Dawson]

Ok thanks for the replies.

I think the tram is out, so I'll have to readjust it tomorrow. Found a good tutorial on Youtube!

However, I'm not fully convinced tramming is the cause. The fact the holes have a larger diameter entry side than exit side makes me think there is excessive play in the quill.

I'll try your recommendation Jim and post back with the results.

Thanks

I'm not convinced either, but can't hurt to check it. Are you making a couple of finishing passes in the bottom of the hole? I find that's helpful with a lot of stickout.

[Jim Dawson]

spiral drilling? do you mean boring? the only times i have had that issue it has been tooling or feeds and speeds.
I have also heard boring called offset reaming. lol

No, spiral drilling (or maybe pocketing). The path of the endmill is a helix as it creates the hole, then normally will make a full circle final pass to flatten the bottom.