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- Thread starter HTovar
- Start date
- Replies 11
- Views 1,217
Mark Rand
Diamond
- Joined
- Jul 9, 2007
- Location
- UK Rugby Warwickshire
Because you haven't cut deep enough yet...
G
guest
Guest
...or you're dragging the insert across the crest on the retract.
1953chevB
Cast Iron
- Joined
- Jul 31, 2020
what is the exact thread call out
ChipSplitter
Titanium
- Joined
- May 23, 2019
- Location
- Maybe
I'd say you need a few more drags on that weed you're smoking.
TeachMePlease
Diamond
- Joined
- Feb 11, 2014
- Location
- FL
maybe an ID I OT?
John Garner
Titanium
- Joined
- Sep 1, 2004
- Location
- south SF Bay area, California
The common screwthreads -- Unified, ISO Metric, and US Standard -- are supposed to have flats at both the crests and roots.
FredC
Diamond
- Joined
- Oct 29, 2010
- Location
- Dewees Texas
You did not provide enough info. Maybe the reason for the non helpful replies.
If your 20 pitch thread is an OD screw, both observations point the same direction. You need to take a couple more passes and dial in a little deeper.
If you are doing an ID thread like a nut, I will take a guess that improper clearance on the threading tool/bar is causing some drag on your thread minor and enlarging it. First guess it would not be a cutting action more like rubbing and the peaks of the threads beside being too large will have a rougher nasty finish. This could happen before your major diameter and pitch diameter get finished. Look for rubbing on the bottom of your tool holder or insert if the one chosen is too large. Tool below center could contribute to this or be an outright cause.. Generally I hate to grind on an other wise good tool holder, but in a pinch you could grind off some material on the area rubbing. If the tool is below center shimming or adjusting the tool could fix it without alterations to the tool.
If your 20 pitch thread is an OD screw, both observations point the same direction. You need to take a couple more passes and dial in a little deeper.
If you are doing an ID thread like a nut, I will take a guess that improper clearance on the threading tool/bar is causing some drag on your thread minor and enlarging it. First guess it would not be a cutting action more like rubbing and the peaks of the threads beside being too large will have a rougher nasty finish. This could happen before your major diameter and pitch diameter get finished. Look for rubbing on the bottom of your tool holder or insert if the one chosen is too large. Tool below center could contribute to this or be an outright cause.. Generally I hate to grind on an other wise good tool holder, but in a pinch you could grind off some material on the area rubbing. If the tool is below center shimming or adjusting the tool could fix it without alterations to the tool.
Not a lot of details to unwind this mystery but I'll try anyway.
You are in Texas so I'll assume this is oil field related I'll also assume this is for a big boy like Baker/Haliburton/weatheaford and you are trying to thread to the spec they provided and when you cut the thread to the spec the test part / gage won't screw on? What they don't tell you when they hand you that spec is that they (in their manufacturing plants) have someone, usually toolflo, grind special profile inserts for standard threads ,im talking acme and UN threads.
To hit their numbers with off the shelf inserts you have to first hit the minor dimension on external threads or Major on internals then start offsetting the Z axis to widen the root of the threads until the gage makes up.
But this is just a guess based off of pretty much nothing, lol.
You are in Texas so I'll assume this is oil field related I'll also assume this is for a big boy like Baker/Haliburton/weatheaford and you are trying to thread to the spec they provided and when you cut the thread to the spec the test part / gage won't screw on? What they don't tell you when they hand you that spec is that they (in their manufacturing plants) have someone, usually toolflo, grind special profile inserts for standard threads ,im talking acme and UN threads.
To hit their numbers with off the shelf inserts you have to first hit the minor dimension on external threads or Major on internals then start offsetting the Z axis to widen the root of the threads until the gage makes up.
But this is just a guess based off of pretty much nothing, lol.
EPAIII
Diamond
- Joined
- Nov 23, 2003
- Location
- Beaumont, TX, USA
OK, first you did not say if this is an internal or external thread. It may also be nice, but probably not necessary to know the diameter.
External thread: And the minor diameter is oversized. The easy answer, assuming that everything else is being done properly, is you just need to cut it deeper. You are doing the basic measure at the PITCH DIAMETER, aren't you? But I would guess you already knew that. So, if this is an external thread AND the pitch diameter is correct, then you are using the wrong insert for 20 TPI. You need one with a smaller flat at the tip so it cuts deeper at the minor diameter while not decreasing the already correct pitch diameter.
If you are not measuring the thread and judging the thread cutting process by measuring the pitch diameter, then all bets are off. If you use the OD and the in-feed distance, it is real easy to get things wrong for a number of reasons. The first one is not deburring the OD after cutting the thread.
Internal thread: And the minor diameter is oversized. The easy answer, again assuming that everything else is being done properly, is you just need to use a larger drill bit or bore a larger hole before threading. And do a proper job of deburring it after cutting the threads. If it is an internal thread and the hole is the proper diameter AND you are deburring it after threading, it is hard to imagine just how the minor diameter could be off.
So, tell us more about what you are doing.
External thread: And the minor diameter is oversized. The easy answer, assuming that everything else is being done properly, is you just need to cut it deeper. You are doing the basic measure at the PITCH DIAMETER, aren't you? But I would guess you already knew that. So, if this is an external thread AND the pitch diameter is correct, then you are using the wrong insert for 20 TPI. You need one with a smaller flat at the tip so it cuts deeper at the minor diameter while not decreasing the already correct pitch diameter.
If you are not measuring the thread and judging the thread cutting process by measuring the pitch diameter, then all bets are off. If you use the OD and the in-feed distance, it is real easy to get things wrong for a number of reasons. The first one is not deburring the OD after cutting the thread.
Internal thread: And the minor diameter is oversized. The easy answer, again assuming that everything else is being done properly, is you just need to use a larger drill bit or bore a larger hole before threading. And do a proper job of deburring it after cutting the threads. If it is an internal thread and the hole is the proper diameter AND you are deburring it after threading, it is hard to imagine just how the minor diameter could be off.
So, tell us more about what you are doing.
