ISSUE Bridgeport Power Drawbar Weak and Buildup/Poor Surface on Shell Cutter Taper 2022/12/5

Machine Shop
#1

Hello, I hope this is in the right place. Last night I was using the Bridgeport and the power drawbar did not sound as strong as it usually does. Regardless, it still pulled the tool in and seemed fine. I was getting some help from others in the space as it didn’t seem to be cutting right 30-60 minutes later, and the cutter began coming out of the taper. Later I noticed some metal buildup/scarring on the top of the taper, I’m not sure if it was there when I started or not.

The shell cutter in question is in the tool cabinet nearest the Bridgeport and has a red “Out of Service” tag on it.

I later tried using the other shell mill and had no issues for the rest of the evening.

#2

In case the tag is not there somehow, it’s the shell cutter with machinist blue one it.

#3

@Team_Machine_Shop

#4

I took a look this afternoon when I was in. The power drawbar did sound a bit weak. I took the cover off and noticed the dial was set to about 4. I increased it to 6 and it was much better. The psi on the side gauge looked normal (between 80-90 I believe).

As for the metal buildup/scarring. What kind of cutting were you trying to do. It appears that you may have been trying to side cut? This milling cutter is generally intended for facing cuts. Horizontal cuts where the cutting surface is parallel to the bottom of the cutter and typically only a couple of thou depth of cut. I think it may be able to cut a 45 degree cut up the side of the insert cutter but no where near as high as the marks are.

Other than that, it doesn’t look like there is any real damage to the cutter although I didn’t cut anything with it.

image
image1190×958 103 KB

image
image1212×1194 145 KB

6 Likes
#5

Thanks for looking at it @Paul_Morley! If I remember correctly the PSI read about 85 when I was there, so that sounds about right.

Regarding cutting, I was doing similar to what you have shown with a green checkmark just not plunging into the material. I was surfacing some square mild steel tube (2.5" x 0.25" wall). Aside from touching off initially just to find the top of the material, all cuts started from the side. Typically about 6-7 thousands depth with oil, 500-1000 RPM, and powerfeed was usually happy 2-4 IPM. Any less than 3 and it sounded terrible and did not cut well, otherwise I didn’t wanna push the machine with any deeper cuts, I think I got up to 10 but decided to back off since 6-7 were giving me a good surface finish.

The buildup/scarring I was talking about was on the taper of the cutter shaft though, not on the side of the cutter shell. I did not do anything deep enough to get near the shell of the cutter.

#6

I see. I misunderstood. You’re talking about this area on the taper of the R8 post?

image
image1160×2012 175 KB

And yes, that would definitely happen if the drawbar was loose. In fact, I’d count it lucky that there wasn’t a more serious issue. It’s definitely vital to have the drawbar tightly fastened. I’m sure that’s fixed now that I increased the pressure.

Thanks for clarification.

1 Like