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16th Apr 2019, 03:20 PM #1Most Valued Member
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How to grind this threading tool?
I need to single-point an M8x1.25 thread on a 9.5mm tube with a 6mm bore. If I use an M8 die the remaining wall thickness will be too thin. I reckon I can do it with a standard 60 degree metric threading tool with a flat ground on the tip. By my calculations the flat needs to be 0.7mm wide. They make gauges for grinding the flat on ACME threading tools, but no such thing exists for what I want to do.
Any suggestions for how to grind the flat reasonably close to 0.7mm wide?
The matching female part will be bored to 7mm then threaded with an M8 tap. This is a non-critical part and will only be finger tight.Chris
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16th Apr 2019, 03:55 PM #2Most Valued Member
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Just touch the tip on your grinder or what ever you are going to use to make the tool.
.7 is pretty wide make a mistake and the job will be bent or sitting on the lathe bed.
Have you considered making the tip less than .7, I would tend to just try a small nose radius.
Are you making the nut first?
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16th Apr 2019, 04:19 PM #3Most Valued Member
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Thanks Peter.
If I use a tip smaller than 0.7mm, won't I need to plunge the tool in further to get the correct thread form? That's what I'm trying to avoid, because it will leave a very thin wall thickness on the tube.
The material will be aluminium, so I'm hoping with a very sharp tool it won't bite and end in disaster. I'm going to use the offset topslide (30 degree) method of thread cutting. Hopefully that will reduce the cutting loads. I imagine it to be just like cutting an ACME thread but with a different thread profile (60 degrees instead of 29 degrees).
Yes, I'll be making the nut first.Chris
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16th Apr 2019, 04:28 PM #4Senior Member
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If you have enough material to do a test run, i would just knock the tip off as per your drawing and give it a go.
Regards
Bradford
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16th Apr 2019, 04:54 PM #5Most Valued Member
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I would suggest reduc8ng the depth of cut by what you take off the tip, if the tip was reduced by .3 and depth should be 1 mm then your depth would be .7.
I would just try it against the nut, if you machine the nut oversize in the bore the same as you reduce the depth of cut you have in essence made a nut to suit your thread, a special.
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16th Apr 2019, 05:27 PM #6Golden Member
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jack620
If you reduce the length of your tool by 0.61mm you will end up with a 0.70 wide tip.
Bob
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16th Apr 2019, 05:34 PM #7Most Valued Member
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16th Apr 2019, 08:37 PM #8
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16th Apr 2019, 08:40 PM #9
For the thread make you own as you describe and knock off the peaks of the nut and all will be fine.
It will be your custom thread, I'm sure there are plenty out there.Using Tapatalk
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16th Apr 2019, 10:42 PM #10Philomath in training
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Why not cut the thread with the plunge method? The depth of thread you want is only 0.5, and 1.25 wide, so it is not a big load on the tool. The advantage is that once you are at depth, if the tip is narrower than the designed thread root, you can just move the compound along a little until you get what you need.
This thread is larger (5tpi) but that is what I did here (2 on the left are my copies; the one on the right is the worn original). The tool tip was 40 thou but the root of this needed to be around 60 something
P1040471.JPG
Michael
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16th Apr 2019, 11:02 PM #11
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17th Apr 2019, 12:58 AM #12
Hi Michael, Guys,
Left hand as well Nice finish.Best Regards:
Baron J.
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17th Apr 2019, 09:10 AM #13Most Valued Member
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