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Post by Deleted on Apr 25, 2009 17:37:24 GMT
I bought some lovely APEX metric diesfrom Penny Farthing Tools some years ago, but didn't use any until I decided to thread the Brit small end 3.0mm instead of the BA spec. The die cut a lovely clean thread, but the nut almost 'floated' onto the bolt! Even after cutting with the die screwed right out, I only got 2.85mm dia. I looked closely at the die(s), and realised they were marked '6g'. Now I haven't been involved with tolerancing since the year dot, but looking in my trusty ZEUS, it appears to confirm my suspicions that '6g' is a very good clearance fit! Can someone confirm my suspicions? No reflection on the supplier, they were clearly marked: I just hadn't noticed it!  |
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Post by havoc on Apr 25, 2009 17:51:11 GMT
I have never seen these markings used for thread. They are destined for holes/axles. I'll have a look at mine if I can reach them in the shop...
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Post by johnstevo on Apr 25, 2009 22:40:32 GMT
That chart is for holes and it's quite a close fit anyway, not loose as you think, in fact on 3mm its -4 to -12 but thats -0.004 to -0.012 of a millimeter, not inches. However all this is irrelevant as your die is marked 6G NOT G6 as in the hole tables.
6G is pretty standard for mass produced threads and at 3 mm is 2.980 max to 2.874 min.
However you have split dies so expanding these should give you close to the max size.
Will your die holder allow this? I have come across holders that won't allow a die to open to max.
John S.
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Post by Deleted on Apr 25, 2009 22:59:42 GMT
Hi John, thanks for the feedback. I made the tailstock die holder to exactly 11/16" so expansion of the die is not possible. I could enlarge it as you suggest but it would spoil the fit of the other dies. The die is cutting at the bottom of the limit (2.85mm) so I suspect I will need a 'special' holder for these dies. No big deal but a little annoying!
JB
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Post by Shawki Shlemon on Apr 26, 2009 8:04:02 GMT
I had similar problem with a 1/4 - 40 die and had to make ( enlarge ) the holder size to permit expansion of the die . Thank God I am not alone with this kind of problem.  My tail stock holder is home made , I drilled and fitted two extra screws to centralise the die in the holder , that is to prevent the die being off centre when expanded . |
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Post by drjohn on Apr 26, 2009 9:02:38 GMT
I must say I'm surprised at you of all people, JB making that fundemental error of not spreading the die. Although, like you and many others, I have tailstock die holders for all sizes of dies, I tend now to use the (I think) Alan Stepney method of puting the die in a standard die holder and pushing it up against the workpiece with the chuck in the tailstock. As long as you have 3 hands (which will be a standard fitting on all humans of the next generation with the DU contamination of our DNA), it's a piece of cake! ;D  DJ |
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Post by Shawki Shlemon on Apr 26, 2009 9:39:52 GMT
It is me again JB , looking at the bolt you are trying to make, I had to make something like that before and my problem was to thread all the way to the end ( I know there are dies that can do that but I don't have them) . I drilled the bolt and tapped the size I want and screwed and loctite a screw and cut the head , perfect finish , threaded to the end and strong, better still no one can tell the difference. Some may call it cheating , I call it improvising . ;D
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Post by drjohn on Apr 26, 2009 10:00:13 GMT
I agree Shawki - I do that quite frequently - God bless loctite!
DJ
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Post by Deleted on Apr 26, 2009 10:03:00 GMT
That's a good call Shawki, I'll remember that one. Pity about DJ though, he's forgotten what I put in the post by the time he gets around to responding.......
JB
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Post by Tel on Apr 26, 2009 20:46:30 GMT
0.15mm under - that's about 0.006" - about where I'd expect a metric die to cut. Mike up a few commercial M3 bolts, you'll see wot I mean.
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Post by Deleted on Apr 27, 2009 8:24:49 GMT
I found this excellent technical reference which clarifies everything: www.boltscience.com/pages/screw8.htmIt would appear that '6g' is a middle tolerance range, using a similar nomenclature to the table in the ZEUS book. If we want to do better then we should look for 'h' rated tooling, confirming my original suspicions! Tel, I have reminded myself from the drawings that the 'undersize' outside diameter on metric ODs is due to the deliberate truncation of the thread form (h/8). JB |
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jackrae
Elder Statesman
Posts: 1,333
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Post by jackrae on Apr 27, 2009 8:25:19 GMT
Simply,
Aren't we all missing something here.
Your presumption is that the die is cutting the thread with too small an OD.
It may well be doing so, but on what basis are you presuming that your nuts are OK (no inuendo intended) maybe they are too large an ID
jack
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Post by Deleted on Apr 27, 2009 8:28:41 GMT
Jack, see my previous post: mind you I'm quite sure there is a bit of nut slack as well!
JB
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Post by ettingtonliam on Apr 27, 2009 8:46:32 GMT
JB
Pardon my ignorance, but you have used the metric die in an 11/16 die holder. Are metric dies made to fit imperial holders, or is there a separate range of metric die holder sizes which they should be used with?
Richard
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Post by Deleted on Apr 27, 2009 8:50:51 GMT
Richard, it may be a case of my ignorance too, but the APEX die is exactly 11/16" dia so I went ahead and used it without thinking about it! I have concluded that there is nothing wrong with the die or the holder, it appears to be a simple tolerancing issue, unless someone knows different......
JB
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Post by kneedeepinswarf on Apr 27, 2009 10:12:01 GMT
JB Pardon my ignorance, but you have used the metric die in an 11/16 die holder. Are metric dies made to fit imperial holders, or is there a separate range of metric die holder sizes which they should be used with? Richard Metric dies are available with outside diameters to both metric and imperial standards. Most UK suppliers seem to sell the imperial ones, presumably because they assume most users will have imperial die holders. It is usual to make the die holder with a larger diameter recess than the die, to allow for adjustment, although I have come across commercial holders that have not had this clearance provided. This can be troublesome as some dies, especially cut-thread types can have a wide tolerance on the O/D and will not always fit such holders easily. In "The Amateur's Lathe" by L.H.Sparey. is given a design for a tail-stock die holder where the diameter if the recesses is given as 1/64" over the nominal O/D of the die, for 13/16" and 1" dies, which would appear to be about right. When using a tail-stock die holder, some error can be introduced when the die is expanded or collapsed by the adjusting screws as this tends to, in effect, put the axis of the die out of line with that of the lathe. This can result in a undersized thread. The only commercial die holder that I have seen which addresses this problem is the one sold by Arrand Engineering, where the holder can be adjusted for axial position after the die itself has been adjusted. I once made a tail stock die holder of the solid type and was troubled by slack threads, I later modified it be similar to the Arrand holder and have had no further problems. Another cause of slack threads I have found is that when the die is expanded by the conical centre screw of the holder, the die can be twisted slightly by the action of the screw, resulting in thin threads; I now always check for this by laying a steel rule across the face of the die after adjustment. Lionel |
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Post by drjohn on Apr 27, 2009 11:15:35 GMT
.... Pity about DJ though, he's forgotten what I put in the post by the time he gets around to responding....... JB Forgive me father JB, but I do not understand what the f**k you're on about DJ |
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Post by ettingtonliam on Apr 27, 2009 13:46:37 GMT
Lionel
OK that answers my question, I'd just wondered whether it was simply a case that the imperial die holder wasn't giving enough room for the metric die to open fully.
When I'm using the tailstock dieholder, with my machinery there's probably enough free play in the tailstock barrel to let everything self centre. One of the occasions when a bit of slack can be beneficial! Using all 3 screws in the dieholder helps take out the twist, but sometimes I have to put shims at the back of the holder so the die can bed down squarely.
Richard
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My tail stock holder is home made , I drilled and fitted two extra screws to centralise the die in the holder , that is to prevent the die being off centre when expanded .
