PDA

View Full Version : Question about beveling pipe on a my lathe ( the angle)



DemonSpeeder
03-04-2013, 11:15 PM
I have been using my lathe to bevel pipe/tube test coupons. The sections very from 2'' -6.5" diameter pieces and different wall thicknesses... from xxh, xh, 1/4"- 3/8"-!/2" wall pipe/tube. I have my compound slide set at the angle to create a 37.5 degree bevel on the pipe/tube. I don't really know for sure the actual C/S angle is because there no #'s in the area. The problem is that even though my sections have 37.5 degree bevel angle, the included bevel seems way too wide. For example 1/4'' wall would have close to an inch wide bevel at the outer diameter between the two sections. When I see pictures (online etc) off tubing/pipe relatively the same diameter and wall thickness the included gap is much smaller. Maybe 1/2'' wide on the outside diameter. I am basically doing much wider "cap" passes than I think should be... Any idea's about what i am doing wrong??

welds4d
03-04-2013, 11:19 PM
the 37 deg angle is off of square, or in other words, off of 90 deg. Your compound will read 53 deg. The 1/2 deg doesn't matter much.

DemonSpeeder
03-04-2013, 11:33 PM
See that's what is confusing me... the pipe/tube itself is showing a 37 degree bevel, if I change the C/S angle it's going to change the bevel angle... how much tolerance is there in the actual bevel angle??

Winmac
03-05-2013, 12:15 AM
i'm just grasping here but Is it possible your measuring the cut pipe bevel incorrectly, http://www.rjsales.com/products/ansi_asme_flanges/misc/m.html

When i cut bevels in a lathe i would rotate the work in reverse and cut on the back side of the pipe with the compound set a 37 deg.

DemonSpeeder
03-05-2013, 12:29 AM
I think I am... I rest the straight edge,ruler part of my protractor against the inside of the pipe/tube and angle shows 37-38 degrees...tried my two different protractors as well...

welds4d
03-05-2013, 07:58 AM
Same concept as I mentioned. When reading the pipe angle off of the axis of the pipe it will be 53 deg. To measure 37 deg, you want your straight edge across the cut end of the pipe. If I remember right, you have a good 2 deg tolerance. And for practice coupons the tolerance is whatever you're comfortable with. If you can weld it with a 30 deg bevel, you can do it with a 37.

Kelvin
03-05-2013, 08:27 AM
I think I am... I rest the straight edge,ruler part of my protractor against the inside of the pipe/tube and angle shows 37-38 degrees...tried my two different protractors as well...

If you measure it like this:

http://www.gowelding.org/images/6G_Pipe_Coupons_Rechecking_Bevel_Angle_With_Protra ctor.jpg

it should be 52.5° not 37.5°

You should be measuring the 37.5° off the square cut at the end of the pipe like this:

http://www.wermac.org/images/root_face.gif

DemonSpeeder
03-05-2013, 11:05 AM
Ok... 1st pic shows how I measure the bevel, second shows the same bevel..either way it shows the same bevel measurement..37.5.... 3rd shows the difference..protractor angle is set at 52 degrees...I am going to reposition my C/S on my lathe to get a 52 degree angle...

DemonSpeeder
03-05-2013, 01:17 PM
Soooo..I spun the C/S around (knob towards headstock) set it to cut a 52 degree bevel with the protractor and ironically the now C/S is showing that it's set at 37-38 degrees.... here are some pics... same piece of tube used as above pics...the included bevel gap is now a 1/2" ... before it was close to 3/4"...

Kelvin
03-05-2013, 02:12 PM
90° – 52.5° = 37.5°

DemonSpeeder
03-05-2013, 04:24 PM
I understand it now... Thanks for the help guys..:D