Havin Trouble Cutting Threads Correctly

I think T Bredehoft and pdentrem nailed it. If you're using the built in protractor to set the compound angle, those usually measure degrees off of parallel with the ways. What you want is 29-30 degrees off the direction of cross slide travel, or 60-61 degrees off parallel to the ways. You may need one of these to set the angle with.

Tom

480.2748.jpg
 
Yes, in looking at your photo again, if the compound is set at 60 degrees and you are advancing the feed with the compound, you will get a pattern like that. If you look closely at the right hand side of the threads, you should be able to see a series of small steps, each step equal in length to the amount of feed you use for each pass.

The compound should be set at 30 degrees or less. At 30 degrees you should be following the previous cut on the right hand side. If you set slightly less than 30, you will make a fine cut on the right as you remove material from the left. This is why many operators prefer to set the compound around 29 to 29-1/2 degrees. Using the cross feed to advance the feed or running the compound at significantly smaller angle than 30 degrees can cause chatter when cutting the thread as you are cutting both sides of the thread at once.

Bob
 
Could you post a pic of your set up from above the compound?
 
+1 on the compound setting, even on my 1950's Logan, you start perpendicular to the ways, so at 90 degrees. To get to 29 degrees, you actually set the protractor based at 61 degrees. If I were to set it to 30 degrees my threads would look like yours.
 
If you use the gauge correctly and the tool bit has a true 60 degree point and is 90 degrees to the the shaft you are threading, both sides will be even no mater what angle the compound is set at if you set and lock the compound first. The picture of the thread setting tool shows 2 v notches on the edges. You placed one flat edge against the shaft and place your threading tool bit point in the v facing the bit and aline the bit in the v. If the sides of the bit fit in the v it will be 90 degrees to the shaft. From your picture it would not be straight. I would like to see a picture of your bit lined up this way.

Sent from my Venue8 3840 using Tapatalk
 
Handy4563 said:
If you use the gauge correctly and the tool bit has a true 60 degree point and is 90 degrees to the the shaft you are threading, both sides will be even no mater what angle the compound is set at if you set and lock the compound first. The picture of the thread setting tool shows 2 v notches on the edges. You placed one flat edge against the shaft and place your threading tool bit point in the v facing the bit and aline the bit in the v. If the sides of the bit fit in the v it will be 90 degrees to the shaft. From your picture it would not be straight. I would like to see a picture of your bit lined up this way.

Sent from my Venue8 3840 using Tapatalk
Click to expand...
That was my original assumption as well, but a closer look at the OP's thread shows a 90 deg. or close angle between the two sides of the thread. This would happen if the compound were set at 60 degrees. The right side of the tool will cut a taper, 30 degrees to the spindle axis or 60 degrees to the perpendicular. The left side of the tool cuts the 30 degree angle for a total of 90 degrees included.

Were the compound angle set properly and the tool angle set wrong, the included angle would be 60 degrees.

Bob
 
Ray,

As already mentioned, an overhead pic of the compound/tool post/tool/work piece relationship that gave the results pictured in your opening post sure would eliminate a lot of guessing.

Tom
 
higgite said:
I think T Bredehoft and pdentrem nailed it. If you're using the built in protractor to set the compound angle, those usually measure degrees off of parallel with the ways. What you want is 29-30 degrees off the direction of cross slide travel, or 60-61 degrees off parallel to the ways. You may need one of these to set the angle with.

Tom

480.2748.jpg
Click to expand...
Yes I used a protractor just now and my compound when set on 30 degrees is 30 degrees to the work piece sticking out of the chuck.
 
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