Bridgeport/cutting Question

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Mike8623

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OK guys Let me state this right off the top, I am a hobbiest and a novice when it comes to machining and my Bridgeport, I am not a professional. I just got my head took off for asking this question on another forum.

I bought a used Bridgeport about 3 years ago that belonged to a Gent who had died. The Machine is a Bridgeport series 1 2hp. It was covered in aluminum swarf, I mean really covered. I cleaned it all up and just now have set it up in my shop and have begun to use it. It runs just fine and just need a little TLC.

I am cutting a piece of 8620 steel with a 1 inch HSS end mill with a 3/4 shank. I'm running 400 rpm taking a .050 cut. The ram is all the way back and locked, the spindle is all the way up and locked, the x axis is locked and I'm using the y axis in and out to move the cutter in and out of the work. I also using the z and moving it up into the work versus pushing the spindle down. The chips coming off are the same color as the metal I'm cutting to a bronze color.

My problem is when I move the cutter into the work it cuts just fine, but I can start seeing it taking less of a bite about half way through and then when I'm exiting the work the cutter will just fall off the work about .020. I then back the cutter back through the work and it takes out the rest where it fell off. It appears when I enter the work the cutter is being forced up and not taking the full cut that it should. I can see the spindle wobbling a bit at the top as the machine is running. Am I taking too big a cut, Does my machine need new bearings or am I doing something else wrong.......Can someone help?

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8620 is nasty stuff. I'd run about 40 surface feet, or 150 RPM with a 1 inch cutter. Mild steel should be cut at no more than 90 surface feet per minute, at 400 you are well beyond that. If your cutter has survived, (not rounded over on the corners) it should work at 150 RPM, but if it's worn, no speed will do any good at all.

Is the cutter in a Weldon type holder with a set screw? or a collet? If a collet, the cutter could be being driven up. but that wouldn't allow it to come back down. Thats a puzzle.

Hope your head doesn't fee like it's been bitten off, I'd like to tell you everything is good, and you've done well.
 
T Bredehoft said:
8620 is nasty stuff. I'd run about 40 surface feet, or 150 RPM with a 1 inch cutter. Mild steel should be cut at no more than 90 surface feet per minute, at 400 you are well beyond that. If your cutter has survived, (not rounded over on the corners) it should work at 150 RPM, but if it's worn, no speed will do any good at all.

Is the cutter in a Weldon type holder with a set screw? or a collet? If a collet, the cutter could be being driven up. but that wouldn't allow it to come back down. Thats a puzzle.

Hope your head doesn't fee like it's been bitten off, I'd like to tell you everything is good, and you've done well.
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Mike8623 said:
OK guys Let me state this right off the top, I am a hobbiest and a novice when it comes to machining and my Bridgeport, I am not a professional. I just got my head took off for asking this question on another forum.

I bought a used Bridgeport about 3 years ago that belonged to a Gent who had died. The Machine is a Bridgeport series 1 2hp. It was covered in aluminum swarf, I mean really covered. I cleaned it all up and just now have set it up in my shop and have begun to use it. It runs just fine and just need a little TLC.

I am cutting a piece of 8620 steel with a 1 inch HSS end mill with a 3/4 shank. I'm running 400 rpm taking a .050 cut. The ram is all the way back and locked, the spindle is all the way up and locked, the x axis is locked and I'm using the y axis in and out to move the cutter in and out of the work. I also using the z and moving it up into the work versus pushing the spindle down. The chips coming off are the same color as the metal I'm cutting to a bronze color.

My problem is when I move the cutter into the work it cuts just fine, but I can start seeing it taking less of a bite about half way through and then when I'm exiting the work the cutter will just fall off the work about .020. I then back the cutter back through the work and it takes out the rest where it fell off. It appears when I enter the work the cutter is being forced up and not taking the full cut that it should. I can see the spindle wobbling a bit at the top as the machine is running. Am I taking too big a cut, Does my machine need new bearings or am I doing something else wrong.......Can someone help?

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Hey, Thanks so much for the info I'll take your advise The cutter moving up and then down has me stumped also. Anyone else have any ideas. Your response was just fine, on the last forum I was flat out told it was basically for professionals and I was scoffed at for being a hobbiest.
 
I thought they were pretty polite in their response to you. I just got the impression you did not like what they were saying.

I know this is not what you want to hear, but JR gave you the right answer(s) to your question. Way too big of cutter for basically a machine that not sturdy enough for the cut you are attempting.

Even though I have 1" end mills, I don't use them, but instead prefer multi-index cutters....they cut much better for large WOCs. In your case, JR suggestion of going to 1/2" end mill or smaller is spot-on. As well as slowing down you speed.
 
CraigB1960 said:
I thought they were pretty polite in their response to you. I just got the impression you did not like what they were saying.

I know this is not what you want to hear, but JR gave you the right answer(s) to your question. Way too big of cutter for basically a machine that not sturdy enough for the cut you are attempting.

Even though I have 1" end mills, I don't use them, but instead prefer multi-index cutters....they cut much better for large WOCs. In your case, JR suggestion of going to 1/2" end mill or smaller is spot-on. As well as slowing down you speed.
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I apologize if you read me wrong.....I don't mind constructive critisism. It's not that I didn't want to hear what he said, it was the condescending and looking down on someone with less experience way he said it. Then when someone said everyone there were professionals and how much money they made for just giving their opinions and basically that I should feel lucky that I was being blessed by them just for coming down off their lofty perches and speaking to a lowly gent, A hobbiest as one person put it that I should just bow my head and pray. Now all that being said, that is the way I took it. I'd like to get by all that and look forward to more friendly responses on this site, like the first one that was first posted. Come-on guys I'm just looking for some help here. If I'm feeding my work to fast, tell me. If I'm using the wrong cutter just tell me, If I'm milling to fast, just tell me. If I'm doing else wrong just tell me and then offer some remedies if you have any. Don't tell me I'm lucky I got off so easy. All I want is a little help.
 
Mike8623 said:
I apologize if you read me wrong.....I don't mind constructive critisism. It's not that I didn't want to hear what he said, it was the condescending and looking down on someone with less experience way he said it. Then when someone said everyone there were professionals and how much money they made for just giving their opinions and basically that I should feel lucky that I was being blessed by them just for coming down off their lofty perches and speaking to a lowly gent, A hobbiest as one person put it that I should just bow my head and pray. Now all that being said, that is the way I took it. I'd like to get by all that and look forward to more friendly responses on this site, like the first one that was first posted. Come-on guys I'm just looking for some help here. If I'm feeding my work to fast, tell me. If I'm using the wrong cutter just tell me, If I'm milling to fast, just tell me. If I'm doing else wrong just tell me and then offer some remedies if you have any. Don't tell me I'm lucky I got off so easy. All I want is a little help.
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Tom, again I want to thank you for responding. I did look at my cutter and you were right, it is pretty chipped which more than likely is leading to my problem. I change to another cutter (smaller) and a slower speed and see how that works. Thanks to all again.
 
I know what you are saying about the folks over there, but they do know what they are talking about with regards to machining.

Our Bridgeports, though they look it, are not very rigid. The climbing of tool, then falling back is a witness to this. I always calculate my speeds and feeds for the material and cutter used, then back the numbers down from there.

As a hobbyist, I tend to take more light cuts, with a smaller tool. Takes longer, but saves on tool life and machine wear. Things I care about since I am self-financed!
 
CraigB1960 said:
I know what you are saying about the folks over there, but they do know what they are talking about with regards to machining.

Our Bridgeports, though they look it, are not very rigid. The climbing of tool, then falling back is a witness to this. I always calculate my speeds and feeds for the material and cutter used, then back the numbers down from there.

As a hobbyist, I tend to take more light cuts, with a smaller tool. Takes longer, but saves on tool life and machine wear. Things I care about since I am self-financed!
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Thanks Craig.
 
In addition to the advice in the posts above, if your stock is set up in the vise you might try clamping directly to the table to eliminate any issues (movement) with the vise. Welcome to the forum. Pretty tolerant bunch here, they put up with me. Mike
 
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