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Author Topic: When is a Hole not quite a Hole?  (Read 1047 times)

derekwarner

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When is a Hole not quite a Hole?
« on: April 12, 2018, 03:40:10 PM »

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
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Derek Warner

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Illawarra Live Steamers Co-op
Australia
www.ils.org.au

RST

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Re: When is a Hole not quite a Hole?
« Reply #1 on: April 12, 2018, 05:49:44 PM »

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.
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derekwarner

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Re: When is a Hole not quite a Hole?
« Reply #2 on: April 12, 2018, 10:30:59 PM »

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
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Derek Warner

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Brian60

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Re: When is a Hole not quite a Hole?
« Reply #3 on: April 13, 2018, 08:00:08 AM »

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

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Re: When is a Hole not quite a Hole?
« Reply #4 on: April 13, 2018, 09:30:58 AM »

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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Martin [Admin]

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Re: When is a Hole not quite a Hole?
« Reply #5 on: April 13, 2018, 09:43:28 AM »


NB: INOX  =  stainless steel
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derekwarner

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Re: When is a Hole not quite a Hole?
« Reply #6 on: April 13, 2018, 11:06:26 AM »

Yes Martin.... [INOX = suitable for inoxidible - Austenitic steels] or as we know them as the Grade 300 family of stainless steels
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Derek Warner

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grendel

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Re: When is a Hole not quite a Hole?
« Reply #7 on: April 13, 2018, 12:36:54 PM »

for my drilling in stainless I use 0.7mm pcb drills, then push a 0.8mm stainless steel pin through to clean the hole, fortunately I havent required 4mm holes in stainless yet
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terry horton

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Re: When is a Hole not quite a Hole?
« Reply #8 on: April 13, 2018, 04:46:09 PM »

In the toolmaking, med eng and defence eng industries we never used a drill bit for precision holes..... if a hole was too small to be bored it would be drilled within very few thou of the final size and finished with a reamer within the tolerance required.
Many would probably disagree but that's how we did it.
As an apprentice 50 years ago, my instructor always said never trust a drill for finishing precision holes.



Regards
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John W E

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Re: When is a Hole not quite a Hole?
« Reply #9 on: April 13, 2018, 05:02:39 PM »



hi there Derek


When I used to work for a Company who  produce Aircraft engines we used to have a 'standards' room and our measuring instruments had to be calibrated every month.   When was it that you last had your Vernier calipers calibrated?   :-)  I have known that there be a difference in readings between the jaws of the caliper and the actual measuring points of the calipers on the other end - always taught a micrometer for measuring shafts and Verniers for measuring small holes.  Just as a side note on drilling materials, as we had to drill holes for close tolerance we had to first of all pilot hole drill and them ream with a machine or hand reamer.


Whilst working for the industry we had to machine a material called Waspaloy and this has a tendency to grow whilst machining,. we used to have to let it cool down even though we used cooling fluid to machine it.  It still used to contract or move after several minutes of standing.  Hellish stuff to work with.
I wonder if that is what is happening with your drilling of the cogs.


John


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derekwarner

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Re: When is a Hole not quite a Hole?
« Reply #10 on: April 13, 2018, 10:56:10 PM »

Hullo & thankyou both Terry & John...............

We probably went to the same Technical Colleagues in the mid 1960's but on the opposite side if the world %)

Our supervisors told of the same procedure for drilling & reaming.......however we were talking 1/2" diameter +  where we could use Ball Gauges to gauge, then the calibrated outside micrometer to establish the actuals

In those days, we also calibrated the 0-1" M&W micrometer in a tool room at 20 degrees C, then proceeded to our work stations and measured our components at 35 degrees  %%

I have set my trusty 40 year old Polish Vernier caliper to 25.0 mm [4 times] ....each time by comparison the digital caliper reads 25.06

Maybe my eye ball needs calibrating

Derek

 
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Derek Warner

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terry horton

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Re: When is a Hole not quite a Hole?
« Reply #11 on: April 13, 2018, 11:10:33 PM »

Ha yes , the Standards Room nice position if you could get it...... cool in summer , warm in winter..... not like out on the  production shop floor.
Paraffin heaters blowing down the Bay in winter , makeshift card board Fans spinning on the arbor spindle of your milling machine in summer !
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bfgstew

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Re: When is a Hole not quite a Hole?
« Reply #12 on: April 13, 2018, 11:53:42 PM »

A phenomina known as Reuleaux triangle comes to mind from my days as an apprentice. A round drill can produce a triangular hole, (more so when drilling thin materials) when measured it shows the correct diameter but a shaft or bar will not fit.....Google it. Blunt drill, incorrect feed or speed, no lubrication/cooling, the only true way is drill slightly smaller and then ream it out to the required size, watching of course for your tolerances (i always refer to my trusty Zeus book for things like this).
Calibration is always done at 20°C, once it is calibrated most verniers and mic's will be true even in warm temps as the part you are measuring will be near enough the same temp it will only be a few microns out.
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