WhoWhatNow
Well-known member
I have a line on a Bridgeport j head. What should I look for when I inspect the machine. I am a complete machining novice so go easy in me!
Bridgeport mill - how to evaluate?
- Thread starter WhoWhatNow
- Start date
Go to Youtube and search for Tubal Caine. He has an excellent series on machine shop basics and I believe one of the episodes covers evaluating used lathes/milling machines.
The other one that I'd highly recommend is the Darrell Holland Milling Machine videos. He specifically covers how to evaluate a J head Bridgeport.
The last series is the MIT Machine Shop videos. (they're free). However he doesn't spend much (if any) time on evaluating the machines.
Cryptic1911
Well-known member
check the surface of the ways to see if there are still scraping marks in it (shaped like U's) instead of it being shiny and flat.. the scrape marks help hold the oil.
If you can power it up, listen for any bad sounding noises in the motor, and also have them fire it up in back gear to listen to the gearbox. That will be noisier than direct drive mode, but it shouldn't sound like a blender or anything
The table will most likely have some oops marks in it, but just make sure there is nothing too catastrophic, especially in the t-slots as thats where you will be clamping stuff to. Ours has a few plunge cuts into the slots, but nothing all the way through
Check for slop in each axis. There will be some, it's unavoidable, so don't panic. Just take note of how much is there. For example, spin the x-axis crank a few turns, then loosen the dial and lock it at 0, then spin the crank the other direction to take up the slop. You'll feel it free wheel and then get tight as it grabs. Look at the dial and see what it reads now. The bridgeport we just picked up has .015 in X axis, .017 in Y axis, and I think .015 in the Z axis, which isn't bad at all. If the machine has a digital readout, the slop really isn't that critical as the dro will read table movement on its own without the dials on the cranks. Some people talk about 1/4 turn or more before it grabs, but that seems excessive to me
Check and make sure the auto downfeed is working. Sometimes the selector shaft? that sticks out of the manual fine feed crank on the front left of the head is broken off, and the crank is missing, so just check all that stuff.
If there's an oiler, try pumping it a few times to see if oil runs out anywhere. if you get runs all on the left side, and nothing on the right, then it's quite possible that the line to the right side is plugged, etc. There will be lines to each side of the ways for x,y, and z.
If the motor is 3 phase, you can still run it on 220 single phase, as long as you have a phase converter of some kind. Rotary and static phase converters only get you about 2/3 of the rated power, but if you use a vfd / variable frequency drive, you can get full power, and also vary the rpms of the motor
If you can power it up, listen for any bad sounding noises in the motor, and also have them fire it up in back gear to listen to the gearbox. That will be noisier than direct drive mode, but it shouldn't sound like a blender or anything
The table will most likely have some oops marks in it, but just make sure there is nothing too catastrophic, especially in the t-slots as thats where you will be clamping stuff to. Ours has a few plunge cuts into the slots, but nothing all the way through
Check for slop in each axis. There will be some, it's unavoidable, so don't panic. Just take note of how much is there. For example, spin the x-axis crank a few turns, then loosen the dial and lock it at 0, then spin the crank the other direction to take up the slop. You'll feel it free wheel and then get tight as it grabs. Look at the dial and see what it reads now. The bridgeport we just picked up has .015 in X axis, .017 in Y axis, and I think .015 in the Z axis, which isn't bad at all. If the machine has a digital readout, the slop really isn't that critical as the dro will read table movement on its own without the dials on the cranks. Some people talk about 1/4 turn or more before it grabs, but that seems excessive to me
Check and make sure the auto downfeed is working. Sometimes the selector shaft? that sticks out of the manual fine feed crank on the front left of the head is broken off, and the crank is missing, so just check all that stuff.
If there's an oiler, try pumping it a few times to see if oil runs out anywhere. if you get runs all on the left side, and nothing on the right, then it's quite possible that the line to the right side is plugged, etc. There will be lines to each side of the ways for x,y, and z.
If the motor is 3 phase, you can still run it on 220 single phase, as long as you have a phase converter of some kind. Rotary and static phase converters only get you about 2/3 of the rated power, but if you use a vfd / variable frequency drive, you can get full power, and also vary the rpms of the motor
Watchwatch
Member
- Joined
- May 12, 2012
- Messages
- 21
+1 for Tubal Caine. He is a retired shop teacher. His videos are packed full of information and he is very articulate.
OP
WhoWhatNow
Well-known member
Thanks for the tips so far. I going a 1pm to check it out. If I have a chance I'll take a look at the Tubal Caine vids before I go. I have heard his vids are really good I just haven't had a chance go watch them yet.
OP
WhoWhatNow
Well-known member
This should be an R8 spindle correct?
bczygan
Well-known member
Yup.
Cryptic1911
Well-known member
yeah j-heads are r8, m-heads I think were b&s or morse usually
Be sure to post some pics.
OP
WhoWhatNow
Well-known member
Now to get it home
Cryptic1911
Well-known member
Nice! looks like a 12br with a 12" knee and 42" table? how was the slop / wear in the screws when you turn the cranks? and is the motor 1 or 3 phase?
When you pick it up, check the side door for the fine feed crank, if its not there, ask and they may have it.
As for moving it, You'll want to lower the table, rotate the head 180deg so it's upside down, and then bring the table back up to it and support on the table with a block of wood. That way it lowers the center of gravity. Doing this will require you to tram the head later on, which is locking an indicator in the spindle and then measuring in 4 directions to the table get the head dead flat, or as close as you can get. Otherwise, you'll end up cutting at an angle. Just lining up the - lines on the 0 mark doesn't cut it. You'll want to learn how to do it manually with a dial test indicator, but if you want, you can spend $100 and buy a spindle square to do it the "easy" way. Tubalcain / mrpete222 on youtube has some videos on how to do this. It's not real hard, its just kind of a pain in the ***
When you pick it up, check the side door for the fine feed crank, if its not there, ask and they may have it.
As for moving it, You'll want to lower the table, rotate the head 180deg so it's upside down, and then bring the table back up to it and support on the table with a block of wood. That way it lowers the center of gravity. Doing this will require you to tram the head later on, which is locking an indicator in the spindle and then measuring in 4 directions to the table get the head dead flat, or as close as you can get. Otherwise, you'll end up cutting at an angle. Just lining up the - lines on the 0 mark doesn't cut it. You'll want to learn how to do it manually with a dial test indicator, but if you want, you can spend $100 and buy a spindle square to do it the "easy" way. Tubalcain / mrpete222 on youtube has some videos on how to do this. It's not real hard, its just kind of a pain in the ***
E.Marquez
Well-known member
Ship it to me (fraight pre paid of course) I will evaluate it for a few months (72 or so) and let you know what i find.
