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Not sure why - they're just pdf files. Maybe try right clicking and choosing "save file as" and save it on your desktop, then try opening it there. If that fails, PM me.
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Thread cutting dilema?
- Thread starter porthos
- Start date
Not sure why - they're just pdf files. Maybe try right clicking and choosing "save file as" and save it on your desktop, then try opening it there. If that fails, PM me.
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I know this one to be of high quality and the price is good: https://www.amazon.com/Mitutoyo-950...3687&sr=8-1&keywords=mitutoyo+60+degree+gauge
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I was searching my computer for a pic of a screw with the features I mentioned - chamfer, thread relief. I couldn't find the one I was looking for but I found this one and I hope it sort of gives you an idea of what I meant. This is an 8mm Class 3 thread in 1144 Stressproof steel. It has a 30 degree chamfer at the end X 1-1/2 threads (most of it is on the other side of the screw - sorry) and a thread relief. It was cut with a Rex AAA cobalt HSS threading tool with 15 degree relief angles and the thread is as it comes off the lathe, no filing or anything. The thread relief is about 2-3 threads wide and ends in a clean shoulder; made with a P1-N parting tool. For those of you with calibrated eyeballs, the depth of the thread relief is 0.003" deeper than the minor diameter.
Hope this makes things clearer.
Hope this makes things clearer.
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I think there was a miscommunication there. I wasn't looking for the fishtail(got one) but the attachment like this:
https://www.amazon.com/Starrett-392...=2025&creative=165953&creativeASIN=B000JERN5C
Outta stock and possibly outta production. Personally the one thing I don't like is trying to hold the fishtail in alignment while trying to weasel everything else. Was a really good idea and might have even seen one in the old machinist boxes I've looked through but didn't know what it was.
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So the other factor amongst the many is the type of steel you are trying to thread it would seem. What's the best steels for single point threading?
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Doesn't really matter. If you can turn it, you can thread it.
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Sorry, my mistake. I grind my HSS threading tools very accurately so I don't bother to align it with a fishtail. I use an accurately turned and faced piece of steel and butt it up against the chuck face on one end and the side of the tool on the other end. This gets the tool aligned perpendicular to the work piece. This works for me. I use the fishtail to check my 60 degree angle when grinding. I also use it to align my tool when internal threading.
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I think the disparity is related to the tool used; if your tool is HSS (and that's the old style), the easiest sharpening
is to make it a left-cutting or right-cutting tool, only ONE of the two edges of the tool is at the optimum height for cutting.
With a carbide insert, a one-edged insert might have a chipbreaker on the left edge but not the right. A symmetric
two-edge insert will cut left and right flanks equally (but it's problematic to include a chip breaker).
For fine vee threads, with HSS tool, and for the relatively heavy chip loads that a single-point tool
does most efficiently, the 29.5 degree setting is still a good choice. If you need special accuracy,
the sideways-load-flex issue might point you to 90 degree plunge cutting (but don't expect the chip
to come out as a nice curl).
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Not disagreeing at all with the above but my simple understanding about the crossfeed vs compound feed thing is related to tool loads, cutting forces and heat distribution.
When feeding straight in with the cross slide, both flanks of the tool are engaged in the work and as you go deeper into the thread, cutting forces climb with flank engagement. This generates heat, which affects tool wear and tool life. This is not a big deal in a hobby shop and many of us do feed in with the cross slide using both HSS and carbide inserts. However, this works best for fine threads (maybe 20 tpi or greater) because the degree to which both flanks are engaged is limited.
Feeding with the compound causes most of the cutting to be done by the leading edge of the tool, be it left or right handed. This keeps cutting forces and heat generation lower while also allowing for better chip clearance. Most (not all) threading inserts and almost all HSS tools (except custom ground tools) have a flat top rake so chip clearance is very much improved when only one flank is engaged. One way to improve this on a HSS tool is to grind 5 degrees of side rake; if you only feed with the compound then this is a very good option. Of course, you will need to grind LH and RH tools this way.
Many of us use both methods in combination. We use the compound to do most of the thread cutting and then use the cross slide to feed in the last few thou to clean up both flanks of the thread. This actually works rather well, especially with a sharp HSS tool.
In terms of which is better, both work. For most of us with manual lathes that thread at low speeds I suspect heat and tool life will not be greatly affected either way. I use the cross slide to thread on my Sherline lathe and the compound to thread on my Emco lathe and I don't see a whole lot of difference in thread form. What does make a difference is the tool. I find my HSS thread tools produce much cleaner and more accurate threads than does my Carmex carbide threading inserts. Nothing against carbide or Carmex; its just that I have some really good HSS tools, that's all.
When feeding straight in with the cross slide, both flanks of the tool are engaged in the work and as you go deeper into the thread, cutting forces climb with flank engagement. This generates heat, which affects tool wear and tool life. This is not a big deal in a hobby shop and many of us do feed in with the cross slide using both HSS and carbide inserts. However, this works best for fine threads (maybe 20 tpi or greater) because the degree to which both flanks are engaged is limited.
Feeding with the compound causes most of the cutting to be done by the leading edge of the tool, be it left or right handed. This keeps cutting forces and heat generation lower while also allowing for better chip clearance. Most (not all) threading inserts and almost all HSS tools (except custom ground tools) have a flat top rake so chip clearance is very much improved when only one flank is engaged. One way to improve this on a HSS tool is to grind 5 degrees of side rake; if you only feed with the compound then this is a very good option. Of course, you will need to grind LH and RH tools this way.
Many of us use both methods in combination. We use the compound to do most of the thread cutting and then use the cross slide to feed in the last few thou to clean up both flanks of the thread. This actually works rather well, especially with a sharp HSS tool.
In terms of which is better, both work. For most of us with manual lathes that thread at low speeds I suspect heat and tool life will not be greatly affected either way. I use the cross slide to thread on my Sherline lathe and the compound to thread on my Emco lathe and I don't see a whole lot of difference in thread form. What does make a difference is the tool. I find my HSS thread tools produce much cleaner and more accurate threads than does my Carmex carbide threading inserts. Nothing against carbide or Carmex; its just that I have some really good HSS tools, that's all.
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