Technical, Techniques, Hints, and Tips > Engineering Techniques and Materials.
When is a Hole not quite a Hole?
derekwarner:
Did I mention my experiences Suttons INOX HSS drill bits? [INOX = suitable for inoxidible - Austenitic steels]
• The American manufactured 10 tooth Grade 304 S/S chain pinion [3.7465 mm chain pitch] had a #2-56 HPGS which I found with a stripped in-hex
• No problem……a Sutton INOX 2.5 diameter with quality cutting fluid dispensed with the #2-56 Grade 304 HPGS & oversize drilled for an M3 x 0.5 tapping
• This, with a new set of Sutton M3 x 0.5 HSS taps was achieved without difficulty…[actually have 2 x M3 tapping's in this chain pinion now]
• So I proceed to bore the same Grade 304 10 tooth pinion [in the ILS Myford super 7] out from the pilot bore of 1/8" to 4.0mm diameter with a Sutton INOX HSS drill bit [cost approx. $7.00] ....[~~ 1500 RPM & very low feed + the cutting fluid skimmed the stainless bore like butter & with a brilliant surface finish]
• I also bored a small brass pinion from 1/8" to 4.0mm bore at the same time
• Got back home & neither the S/S chain pinion nor the brass pinion would slide onto the engine 4.000 mm diameter shaft!
So how do you measure a 4.0 mm diameter HSS drill bit for tolerance?
After an exhaustive search of the Sutton WEB site, it appears this product is manufactured to a DIN338 Standard
After an exhaustive search of DIN338, it appears this diametrical reference is manufactured to a Class of h8
This h8 law of Engineering confirms that the said component in the size range from 3 to 4 mm diameter is to be manufactured to +0.000 to - 0.018mm
I had a sneaking suspicion that all of the above was correct >>:-(, as both of my two components machine drilled with a 4.0 mm diameter Sutton INOX HSS drill bit did not fit onto my 4.000 diameter Saito steam engine shaft
The wonderful people at Suttons in Victoria suggested that this was not possible {-) & if I posted the said Suttons 4.0 INOX HSS drill bit to them by registered Post [$14.00], they would send a replacement at no charge
I have since ordered an M4 HSS parallel reamer [Class H7 +0.00 to +0.018] …yes for $1.82 from the far East…& including free postage
Has anyone encountered a similar issue?.................. Derek
RST:
So what's the tolerance on your Saito shaft? I've argued with folk about asymmetrical tolerances on a few different manufacturing processes over the years. Not sure whether to delve in again LoL.
derekwarner:
Saito documentation is rather sketchy.....they simply nominate that the Engine has a 4 mm output shaft..............my Polish Vernier caliper suggests it is 4.0 mm diameter, my Chinese caliper with a TV set in the corner advises 4.00 mm diameter
I do understand that if I were to drill a blind hole in a rod of brass, the hole would be 4 mm + , however in each case I had a 1/8" pilot hole in the components.....I have not needed or attempted to measure the 2 and 2.5 diameter bits from the same range
They advertise a Step Core [which I don't understand], and display a flame treated/blued tip...the 4 mm drill has a tighter [lower] flute helix spiral angle than standard?, the 2 & 2.5 helix appears to be the same as a standard Jobber drill
Awaiting the reamer..........
Derek
Brian60:
Could it be run out over the length of the drill bit? ie wobble from side to side? I see this in a lot of micro drill bits. If that doesn't play well with the tolerances you mention ( I don't know whether the tolerance covers the length of the drill or the diameter of it or both) But I reckon you have gone the right route anyway - undersize and then ream to finish if you require such close tolerance of fitting.
imsinking:
A two flute drill by it's nature will 'wobble' when piercing , no matter what size pilot you use , (it will follow the contours of the previous drill) especially in brass or a softish material, ending up with an oval 'ole O0 & when you check it with a vernier it will seem to be OK , which wont be the case as the vernier will not indicate ovality . . . a three or four flute drill is the only way to eliminate this , but the S O B's usually cut BIG >>:-( reaming or boring is the only way to achieve proper sizing .
Bill
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