Re: Need help internal threading 13" SB lathe 1 7/8" spindle

carbure2003
 

Cutting at 29 degree enables the face that does not cut to take a burnishing cut on the other face of the thread.

since there was discussions about. Internal threading I moved forward a job I have on the shelf..... manufacturing a telescopic follow rest. I have the knobs left to machine. I machined the internal thread 7/8 NF 14 with my technique.

First picture is the tool held in upside down position.

Second picture is the tool after 20 thou feed. You can see the internal thread.

Third picture is the threading bar at full depth of the thread. You will notice I am working with the steady rest, as the piece of stock overhangs more than 4" from the chuck.

Threading as like the book says means I would have needed a longer threading bar as the compound would have interfered with the steady rest, or chuck if the piece is short and held in the chuck. It means less rigidity and more chances of chatter.

Took less than 15 min to cut the thread, no tap required and I got the fit I wanted.

Saddle, cross slide gibs and compound gibs have to be tight. Forces are upwards. I had some isssues today as it is the first job I do after a carriage clean up (12 monthly routine). I lifted the carriage, Cleaned the slides and wipers. I dismantled the cross slide and made a similar clean up.
I had not finished adjusting the gibs before I started the job.

I hope my pictures help

Guy

---------- Original Message ----------
From: "david pennington via Groups.Io" <davidwpennington=yahoo.com@groups.io>
To: SouthBendLathe@groups.io
Subject: Re: [SouthBendLathe] Need help internal threading 13" SB lathe 1 7/8" spindle
Date: Sun, 27 Jan 2019 08:36:16 -0700


I was taught to set the compound at 29 degrees, not 30. This keeps some pressure on the off-side of the tool and results in a clean cut on both sides of the V. Sent from my Verizon, Samsung Galaxy smartphone -------- Original message --------From: Jim_B <@Jim_B>Date: 1/27/19 08:27 (GMT-07:00)To: SouthBendLathe@...: Re: [SouthBendLathe] Need help internal threading 13" SB lathe 1 7/8" spindle One point I forget.
When your test fitting starts to fit well but still binds, take, what should be your last one or two passes, by feeding out, COUNTERCLOCKWISE, on the cross feed. Note that if you need more than one pass you will not be returning to zero on the cross feed dial.
Since. In threading at 30 degrees on the compound, you only cut on one side of the tool the off side, of the thread, is jagged. Feeding at the end straight out cleans up the off side.

-8
Jim B,

On Jan 27, 2019, at 10:14 AM,


--
Jim B





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