Boring on a vertical milling machine

[Anonymous-0]

Hi,
I have a question for any machinists out there,
I have a stainless steel heavy wall pipe 200mm inside diameter, 150mm long which has 2 flanges welded on it one top and one on the bottom. I want to bore a 1mm step the from the face of the top flange down 10mm On the inside.(Making the first 10mm from the flange face 202mm diameter)

To bore this on a vertical milling machine , bridgeport type, how would I do it, What is the best way to centre it on the machine table?

I cannot use use a lathe because there is a large bracket protruding from the outside wall of the pipe.
Thanks

 

[Anonymous-0]

Am I correct in assuming by your question that your machining experience is limited? Asking this isn't meant to be a put down in any way, we all started the same way, learning the basics. Your project can be a little ornery even for experienced machinist because stainless steel isn't the most friendly stuff to work with. Its stringy, hard to cut without getting hot, etc. Do you have a dial indicator? What type of tooling do you have? How about a boring head? Carbide inserts?

 

[Anonymous-0]

Hi Irv,
Yes my machining experience is limited, i actually thought that I had mentioned that in my post but re reading shows i didnt, anyway I am really enquiring about the procedure and equipment involved in doing this job or something similar , I wont be doing this myself , but this project came up in the place where i work suppose im curiousas to how it could be done especially lining the job up on centre. The job has been sent to a machine shop and I wont get to see how its done, the project is being handled by a different department.

Thanks for your reply

 

[Anonymous-0]

I'm guessing they will chuck it in a lathe using the
inside of the pipe not the outside. It will require a bit of
tweeking to get it trued up assuming the flanges were
not faced off in a lathe when it was made. They will
also go slow and use lots of oil probably sulfered.
Stainless work hardens where a cutting tool passes
thruogh it so the tool will have to cut deep enough on
each pass the cut under the hardened zone left by the
previous pass. Hope this helps.

 

[Anonymous-0]

LM
The centering of the part in the mill is easy to do if you have a dial indicator that will attach to the spindle of the mill. One with a 1.00 travel would be best.The part is placed as close by eye as possible to the center of the spindle. Place the dial indicator probe on the bore of the part at a point fartherest away from you and set the small dial to .500 with the needle on 0.00. With the spindle on freewheel, rotate the spindle 180 degrees toward you and watch the dial as you go.
Let's say the dial is off by +80 degrees. That mean's to get the part centered you have to move the table toward you (Y Axis is front to back) until the reading is +40 degrees. Set the indicator to .500 again and now when you turn the spindle it should stay at .500 or pretty close to it. Repeat the procedure for the left and right side (X Axis is side to side)but don't move the indicator dial this time. You have already centered it; just move the table either right or left till the indicator reads at the same .500 zero again. You might have to do it again to take out the the rest of it using the same pracedure. Hope that makes sense---I've been doing this for 35 years but I've never had to put it in writing. Sure seems a lot harder than showing someone in person. (grin)

 

[Anonymous-0]

LM: Irv gave you a good run-down on the centering basics, but for a 200 mm (8" roughly) tube, you'd probably use a tool called a zero-set--basically a horizontal shaft that a dial test indicator clamps to and slides along it so you can move it out to the edge of the work. It has a vertical shaft to clamp in the spindle and then you proceed as Irv said. More than likely, if this went to a machine shop, they'd either put the pipe in a big lathe with a steady-rest and just let the bracket swing or take off the bracket, turn the step in a lathe and re-attach the bracket.

 

[Anonymous-0]

TimV is correct on the extension for the dial indicator. If you're familiar with them, mine has a magnetic base with double jointed rods so you an get the dial to almost and position. I put a large toolholder in the quill and stick the magnetic base to the outside of it to indicate larger circles. I run a 3 axis CNC bed mill where I work that is programmable for circles, so that job would be easy if I could get the flange clamped flat to the bed.

 

[Anonymous-0]

Irv: just out of curiosity, what do you have for a mill? We've got a HAAS VF-20, and like it. I do most of the programming for it, though I usually let someone else actually run it Here's a link to zero-sets at Enco--what I was referring to is a bit different than a mag-base dial indicator holder. My personal mag-base dial indicator holder is a Noga--not cheap at around $70, but well worth it if you're doing setups in oddball areas, as you can set both axes with one knob.
<ul><li><a href="http://www.use-enco.com/CGI/INSRIT?PARTPG=INSRAR2&PMAKA=891-5413&PMPXNO=3905140">zero-set at Enco</a></ul>

 

[Anonymous-0]

Mine's a Southwestern Industries Trak DPM. It uses conversational language an is quite east to program. Unlike a lot of machining centers and cnc lathes is doesn't use "G" codes in programing. I really like it. SWI is the also the original maker of the "Travadial" dial indicator that mounts on the compound of a lathe bed. A wheel runs along the bed rail and gives quite accurate linear measurement. They used to make the CNC controls for Bridgeport until SWI decided to make their own mill. Bridgeport elected to dump SWI on account of it and make their own controls. That turned out with less than stellar results.