jasonb
Elder Statesman
Posts: 1,209
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Post by jasonb on Mar 26, 2009 19:38:45 GMT
H7 is a measure of the tollerance of a hole, h7 (lowercase) is the tollerance of a shaft, these are quite standard tolerances.
For a 7mm hole a H7 reamer will cut +0.015mm or about half a thou over but not under. And should be mated to an h6 shaft.
If the shaft is to size then a H7 reamer should give a suitable clearance for most things
Jason
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Post by havoc on Mar 26, 2009 20:02:49 GMT
As Jason said, the numbers are part of a tolerance system for holes and axles (ISO-286-1). The numbers indicate the "class": 1-4 are hogh tolerance, 5-11 are standard tolerance and 12-16 are for rough work. The letters indicate where the tolerace is with respect to the nominal size. The upper case is for holes and the lower case is for axles. In principle there are 2 ways to use it: starting where the largers tolerance of the axle is 0 and tolerances are negative (axle has letter h) OR where the smallest tolerance of the hole is 0 and the tolerances are positive (hole has letter H). www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htmwww.wisetool.com/fit.htmThe reamer I find here are always H7. Rather logical as they serve to make a hole that will be the base for a fit. Silver steel is mostly h7 or h6 ground. You should use h6 but I find that h7 works just as well for me. Probably my reamers cut oversize (well, even omre likely is that I make them cut oversize). EDIT: just went looking in my box with reamers and took this pic: The 2 in their tube are indicated on the reamer and on the label as H7, the one pointing to right is chinese and also clearly labelled. I have 3 reamers that have other symbols on them (but can't find them). They came from a shop where they were surprised they found reamers as they didn't remember when they last sold that. IIRC they are labelled "2%" whatever that mean and they look like single flute drills.
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Post by engineernut on Mar 26, 2009 21:35:32 GMT
All the theory in the world will not get away from the fact that in the average hobby workshop if you can get to within a thou in machining you are doing exceedingly well. ;D You can read all the books in the world and know the theory but putting it into practice is another thing. For someone doing their first engine I would imagine the fact of making it is the buzz. The finer points of theory come afterwards. ;D
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Post by Deleted on Mar 27, 2009 8:52:31 GMT
...For someone doing their first engine I would imagine the fact of making it is the buzz. The finer points of theory come afterwards. ;D Spot on engineernut! ;D I am loving every moment of machining the 10V castings etc. Did the boxbed and soleplate last week, drilled and reamed the main bearings last night, and faced-off the standard feet and top surface as well. Horribly basic stuff, but for a noob like me a challenge, and it gave me a huge feeling of satisfaction even though the quality of the work may not be up to much! This involved two firsts for me (a) putting on the faceplate and making some simple clamps to hold the standard, and then (b) using the reamer (that arrived yesterday in the post) - I used it with the tap holder supported by the live centre in the tailstock and it seemed to go OK. As I say, really basic stuff but new experiences for me. All the best, A
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Post by jgb7573 on Mar 27, 2009 8:57:09 GMT
Hi Alasdair. I know exactly what you mean. When you manage to do something you've never done before and it's OK, that's satisfaction.
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Post by engineernut on Mar 27, 2009 17:22:55 GMT
...For someone doing their first engine I would imagine the fact of making it is the buzz. The finer points of theory come afterwards. ;D Spot on engineernut! ;D I am loving every moment of machining the 10V castings etc. Did the boxbed and soleplate last week, drilled and reamed the main bearings last night, and faced-off the standard feet and top surface as well. Horribly basic stuff, but for a noob like me a challenge, and it gave me a huge feeling of satisfaction even though the quality of the work may not be up to much! This involved two firsts for me (a) putting on the faceplate and making some simple clamps to hold the standard, and then (b) using the reamer (that arrived yesterday in the post) - I used it with the tap holder supported by the live centre in the tailstock and it seemed to go OK. As I say, really basic stuff but new experiences for me. All the best, A Hi Alisdair, Glad to hear your already getting satisfaction from the machining part. ;D You will probably make mistakes (I still do now) but you will learn more in practice in a month than just reading theory in a year. An old saying is measure twice and cut once. Very good advice that I wished I had, after 25yrs, followed last week.
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russell
Statesman
Chain driven
Posts: 762
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Post by russell on Mar 27, 2009 20:55:58 GMT
Thanks for the info on tolerances Havoc. None of my reamers are so marked. Most have been collected from government surplus over the last 40 years. I guess I shouldn't be a cheapskate and should buy some new ones but I'll probably just stick to easing thing off with some fine wet and dry or emery.
Russell
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Post by engineernut on Mar 27, 2009 21:14:24 GMT
Thanks for the info on tolerances Havoc. None of my reamers are so marked. Most have been collected from government surplus over the last 40 years. I guess I shouldn't be a cheapskate and should buy some new ones but I'll probably just stick to easing thing off with some fine wet and dry or emery. Russell Probably best way at the end of the day. One still has to make the receiving part. We are not precision engineers talking in 1/10000 of a thou.
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Post by havoc on Mar 28, 2009 15:46:05 GMT
I buy surplus as well, mostly files as that seems to be the only way to find quality files larger than a nail file. But reamers are hard to find here so I have to post order them, mostly in UK.
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Post by engineernut on Mar 28, 2009 18:30:09 GMT
I buy surplus as well, mostly files as that seems to be the only way to find quality files larger than a nail file. But reamers are hard to find here so I have to post order them, mostly in UK. I have accumulated over the years dozens of files of all shapes and sizes. But still use the power file. Normally finish off by hand filing but think why put effort in when one can get a machine to do it. ;D
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Post by havoc on Mar 28, 2009 20:20:07 GMT
Sure, but I find filing (sometimes) therapeutic. When you impose your will by hand on a piece of metal (at it goes well) the satisfaction is high. I love my 18" bastard
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