Cutting Threads for the first time...SB 10k

Well I really screwed the pooch on that one. Messed it all up but at least I know what I did wrong and one of you knew I might. Ericc, the first post thought I might set the compound from the wrong point and I did. I was about 60deg off but tomorrow is another day. I was out in my shop to late and was to tired and did`t pay enough attention . More to come..I`ll post pics of the threads I cut tomorrow...The threads I cut tonight, well let`s just say you won`t be seeing them..WAY to embarrassing ! Thanks for all the input..I need to read up on cutting threads a little more...
 
I use a swing-up toolholder (http://mikesworkshop.weebly.com/swing-up-tool-holder.html),Full profile inserts, cut straight in(perpendicular to workpiece) ,lock the compound, I don't back out the crosslide after each cut, run at 150 rpm,check depth with a thread micrometer and can usually manage class 3 threads . Until I did these things plus what mikey does I had trouble consistently threading. A tight shoulder makes it more difficult since there is little margin for stopping.
 
A tight shoulder makes it more difficult since there is little margin for stopping.

Made me smile ... a shoulder without a thread relief makes for tight sphincters! :eek:
 
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Here is my second attempt at threads to size(1/2-20)...Mind you this was with aluminum. I was running a test before I do it to my project pieces..I have some really close ups of the threads..20180914_204935.jpg20180914_210736.jpgLightly went over them with a file...20180914_211041.jpg20180914_210657.jpg20180914_211300.jpg20180914_211540.jpg
 
Have at it, this part does not hold the wings on a commercial aircraft I suspect.
Chuck stock, set tool as square as possible, touch it off to determine a tool position then thread away until the part measures either over wires or to a ring gauge set.

You likely do not have the equipment to measure a thread in every possible physical aspect of its form.


What all would be needed to check all physical aspects of a thread ? I have and will now use the PeeDee wire thread gauges..and by the way I`m an A&P.....lol
 
What all would be needed to check all physical aspects of a thread ? I have and will now use the PeeDee wire thread gauges..and by the way I`m an A&P.....lol

An Optical Comparator is an excellent tool for this https://www.msi-viking.com/Mitutoyo...MIiM-9h9283QIVA1YNCh0GXg2aEAYYBiABEgIUYfD_BwE
Measurement over wires will give you a Pitch Diameter but assumes that the form is correct to begin with as it can not measure this feature directly without a great deal of work.
Ring gauges will assure that a part is within the limits but also do not measure the form directly, if you were inclined to do so you may produce a thread that measures but has an incorrect form (-:
 
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AJ, see that rough finish on the back side of the thread? As you get deeper, the right side of the tool is not cutting much; it sort of drags. To get a better finish, do not use the compound for the last few cuts. Instead, feed straight in with the cross slide but be careful because the depth of cut is deeper than when using the compound feed. Leave enough room to clean up the threads. This won't make the fit a lot better but your threads will look better.

The other thing that will do that is an inaccurate shape. Check the right side of the tool to make sure it is flat; any rounding or unevenness in the tool face will leave marks.

An accurately ground tool with 15 degree relief angle on the tool will pretty much eliminate this altogether.
 
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AJ, see that rough finish on the back side of the thread? As you get deeper, the right side of the tool is not cutting much; it sort of drags. To get a better finish, do not use the compound for the last few cuts. Instead, feed straight in with the cross slide but be careful because the depth of cut is deeper than when using the compound feed. Leave enough room to clean up the threads. This won't make the fit a lot better but your threads will look better.

The other thing that will do that is an inaccurate shape. Check the right side of the tool to make sure it is flat; any rounding or unevenness in the tool face will leave marks.

An accurately ground tool with 15 degree relief angle on the tool will pretty much eliminate this altogether.


Thanks for the advice but ya know what's funny. Earlier i had sharpened that bit and it cut amazing, the threads were like glass... i didn't resharpen it this time and you can tell. My cuts were to heavy and by the time it fit the hyme joint i didn't have enough material left for a couple finish passes.. All learning experience
 
Here is a screen shot of your tool:

Screen Shot 09-15-18 at 03.12 PM.PNG

Threading tools are form tools. Any deformity in the tool shape is transferred to your work. The accuracy of the 60 degree angle, the relief angles and the nose radius/flat all matter. The included angle of your tool is less than 60 degrees and the right side is scalloped near the tip. It will cut a thread and you may not notice any issues on a class 2 thread but on a precision class 3, yeah, you very well might.

Just so you know, I'm not being critical here. I'm trying to help you troubleshoot your thread form.
 
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Thanks for the advice but ya know what's funny. Earlier i had sharpened that bit and it cut amazing, the threads were like glass... i didn't resharpen it this time and you can tell. My cuts were to heavy and by the time it fit the hyme joint i didn't have enough material left for a couple finish passes.. All learning experience
Materials are not created equally from heat to heat, you can buy a dozen bars one month and they turn just fine, a year later another batch may prove more difficult doing the same operation. Buying random material that is of unknown manufacture is always a gamble when you already have a fixed working process running, often the change to a lower cost material or supplier will cost you in the long run.
 
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