|Michael Gilligan||02/05/2014 17:43:32|
14624 forum posts
Nice Work, Gray !!
I propose a big vote of thanks
|Clive Foster||02/05/2014 18:44:05|
|1950 forum posts|
Well done Graham.
Nice to have practical demonstration that the major conceptual weakness in the inexpensive commercial version is the fixed eccentricity imposed by simply bolting the drill carrier Vee onto the side of the pivot rod assembly with a fixed offset from centre. Its a shame that most of the people making / supplying these devices clearly don't understand what they are making.
I like the improved drill clamp arrangements. Much better than the usual but have you considered the possibility of arranging things so that the whole drill carrier part can be inverted on the pivot unit so the drill only has to be mounted in the carrier once. That way if you do make an error of projection both sides will be the same and the drill will still cut fine. Exact angles aren't super critical, obviously or the commercial rubbish would never work, but identical grinds each side are important. A separate carrier could also make it easier to measure and set projection. Athough it adds parts two carriers, for small and large drills, might well be easier to use. Thats the way I'm going, well actually 3 carriers, should my four facet sharpener ever make it from the back of the envelope into metal along with the rest of "Clives Improved Tool Sharpening System."
The vertical pivot and 5 to 5 drill orientation used in the Picador system is much less sensitive to offset / eccentricity because it needs less correction in absolute terms but orientation is much harder. Especially as the projection has to be derived automatically from the orientation rather than having an measured absolute fraction of diameter value.
No doubt that the American Delta 1296 / Atlas 2195 aka W30 ones are the best of the home shop breeds.
Edited By Clive Foster on 02/05/2014 18:46:27
2314 forum posts
Well done Gray
That encourages me to dig my jig out from the " must try it again ... sometime" heap.
( I imagine that all your drills are in pretty good order any way ......... so if you would like a few (dozen) to "prove" your modification I'm sure that I could " lend" you some! )
|1150 forum posts|
as usual very nice work, and thanks for the advice on improving the jig. I have a similar drill grinding jig myself, so when I finally finish the screwcutting clutch, the jig will become my next project.
|John Haine||02/05/2014 22:37:20|
|2788 forum posts|
Nice work! Where did the basic jig come from please? Would be nice to see an article on this!
3467 forum posts
The 1951 article is by Duplex and runs to quite a few issues
"Making a Twist Drill Grinding Jig"
ME no 2632 2634 2636 2638 2640 2642 and 2644
4861 forum posts
Looks like new life has been given to 100 old jigs, including mine if I can find it.
My recollection is that the joint with the wing nut was very sloppy on mine and I had planned a cross brace to 'complete the triangle'.
John, they can be found from a google search for 'drill grinding attachment' or going to a carboot / garage / yard sale. they used to be quite difficult to sell to model engineers who knwew their reputation but I supect that will now change.
2314 forum posts
"As regards an article I had thought about writing it up but I fear my work is no longer in vogue these days."
NOT IN VOGUE!!!!!!
I think this would be an excellent article and would encourage workshops full of sharp drills across the world!
I guarantee that I will buy any publication carrying such information.
Who are these arbiters of taste and value? - let us know so that we all may shout at them.
|Oompa Lumpa||03/05/2014 10:55:49|
|888 forum posts|
corrected that for you Norman.
|110 forum posts|
4m 57s onwards...
Edited By Martin Millener on 03/05/2014 10:57:28
|John Stevenson||03/05/2014 13:46:06|
5068 forum posts
I'm fortunate that I can sharpen drills by hand but in all fairness I have had a lot of practise, often having to spend possibly an hour a day sharpening drills, most under 3/16"
Re reading that previous sentence I think the critical word is practice but it's something we don all get chance to do. For a start we probably don't own enough drills to get this practice in.
I have noticed that before and after that job I had occasionally I 'lost' the knack of getting the right wrist action.
I have one of these early copies, possibly Taiwanese because of it's age, it's certainly not a genuine Reliance and to be honest I have found it to work OK but slow and fiddly. What I have found though is that if when the 'knack' goes, it's dragged out of retirement and a couple of drills are resharpened with the jig it 're teaches' you the 'knack' or at least it does for me.
So mine whilst spending 99.8% of it's time in a drawer is still a very useful tool.
The next bit might get boring but does contain some useful info.
As well as running the boring shop at a piano company where and don't scoff we had to drill tens of thousands of holes in wood per day to a tolerance of half a thou I also had the design and build the machines to do it. After leaving there I started making division plates as a sideline and don't ask me where they all go but I'm still making the same amount today as I started out doing. Some of the special sets have over 800 holes in them and at a push I can do 10 sets a day so I have probably learn more about small drill than anyone else on this forum.
What I have learnt is than no 'commercially' made drills out there can drill an accurate hole repeatedly and make doesn't come into it. What I have learnt is that none of what I call the commercial spiral swept point drills as shown in the photo's above will repeatedly drill accurate holes.
Note the word repeatedly and this isn't a dig at Graham, he didn't invent the shape.
What happens is that because the centre of the web spins at zero revs being on the centre it rubs and eventually breaks down into small flats or craters, I have stage by stage microscopic photos to prove all this. Subsequently it then starts to pivot away from the centre to find an edge that does cut but is then off position.
It takes a while to do this and anyone only drilling a few holes and keeps their drills sharp will never come across this, we are talking worse case scenario or shed man as opposed to engineer man
This is where 4 facet drills come into action and a correctly ground 4 facet drill can extend the life of a drill by a factor of 4 or 5 but most importantly it also extends it's accuracy by he same amount.
Later I'll sort some photos out of a 3.0 mm drill after drilling 800 holes and its 4 facet brother at the same stage of life. the commercial drill is frankly well past it's useful like and has been for a while but the 4 fact drill can go on to do up to 24,000 to 30,000 holes.
It's not just about replacing a cheap throw away drill, it's about accuracy and life. A drill grinder for doing these small drills in the after-market scene costs around £12,000, not a typo. they still make them and still sell them so it proves there is a demand for them.
Now then, is it necessary ? perhaps not in a home shop but we can learn from this. Lets face it this forum has a greater percentage of armchair machinists prepared to argue the last micron than probably any other.
|John Stevenson||03/05/2014 15:09:04|
5068 forum posts
I think you have done an admirable job and have no problems with the way you have identified and rectified the problems and I am 100% behind you.
I just wanted to point out the short comings of the commercially and read cheap process of the common drill geometry and how it fails.
However I am amazed by your statement " Hole accuracy was not the underlying criteria, grinding the correct angle, with the generally accepted 12 degree relief and a chisel angle of 110 to 115 degrees as recommended by Osborn or Dormer drills was, and I am please to say I have achieved this at minimal cost."
To me hole accuracy and it's placing take preference over what anyone, Osborn or Dormer say about angles.
Modern technology has proved time and again what we were taught by rote and everyone since has repeated parrot fashion is not always the correct way.
Currently one of the most accurate and precise ways of producing holes is with inserted cutter spade drills which have a geometry nothing like Osborn or Dormer dreamed up.
A Derby company is currently making the test centres for Mitutoyo, basically two tailstocks facing each other on a common bed. It's a simple operation for what is a precise operation, the tailstock with ground base is placed in a jig of a machining centre and a 30mm diameter spade drill is fed in. No pilot, no cored hole just straight thru.
No drilling, boring or reaming, just one operation the get a finished hole repeatedly to a tolerance we can only dream of. Mr Myford would be turning in his grave [ pun intended ]
Edited By John Stevenson on 03/05/2014 15:10:34
|Michael Gilligan||03/05/2014 15:49:49|
14624 forum posts
These are absolutely genuine questions, so please don't ridicule me for asking:
I can see that it's reasonable enough to position the machine head, and the clamping fixture, to half a thou in X-Y ... but every other aspect of working to such a tolerance in wood leaves me bewildered.
|John Stevenson||03/05/2014 17:09:54|
5068 forum posts
No it's a perfectly reasonable assumption to doubt this. To be honest when I first went there I thought it was a wind up and it took a couple of days on the shop floor for it to sink in that they were serious.
First off the wood was seasoned beech, maple or hornbeam, we are not talking about old window frames here so very stable. Moisture content was 11% and our own kilns which could handle artic loads could work to plus or minus 1 percent.
Machines were automatic feed cam driven and placed the part into steel vices also clamped by cams. Many of the parts has up to 5 holes in them. Many were bored thru the vices and they would have clearance holes which were then brazed up and redrilled to act as drill bushes or wooden plugs of lignum vite.
Drills were usually held in special high speed spindles running at 200 Hz for 12,000 revs or 400 Hz for 24,000 revs.
Similar the the high speed spindles sold by ARC but these were German Persche <sp> spindles and cost about 1K each, had a working life of 2 years before needing to be reconned.
The shop had 3 ring mains, conventional 440v 50 Hz, 220v 200 Hz and 240v 400 Hz, the latter for the high speed spindles and this power was supplied by two large motor generators at the bottom of the shop. We probably ran in excess of 40 high speed motors
Drills were conventional high quality jobber drills, usually Guring, tanen out of their wrappings and measured then stacked by size. It was normal to get say 1.8mm drills to measure from 1.798 to 1.803mm out of the same packet. They were then ground into 3 point wing and spur drills. When I first went there this was done by hand on a range of grinders which were nothing more than a row of motors with wheels on both ends, no guards and no rests, everything was by eye. later we paid £12,000 for a Christian grinder will all the attachments which speeded the job up no end.
When a drill broke or got blunt. it would be replaced with a new one and the fun would start. A few test pieces would be drilled and checked with go - no go pin gauges with 1/2 thou differences. If you were dead lucky they would get passed by a travelling inspector who did nothing but move from machine to machine taking pieces and testing on pins and gauges. If it was OK he'd sign the machine off.
Usually it was too sloppy so you would try smaller drill from the same batch and even stone the edges with a stone that looked more like a mirror, probably a 100,000 grit. Often you could spend a good couple of hours getting the machine back on line before you moved onto one the inspector had closed off. We had two guys doing nothing but change drills and another guy doing nothing but sharpen drills tools knives and scissors.
We made nothing but piano actions and keyboards for uprights and grands for all the major manufacturers, all they made in hose was the carcases. Steinway, Kemble, Kimble Bechstein, Baldin and Bosendorfer to name but a few of the more famous ones.
We made all our own springs, hammers and all the felt components. Any moving part on an action ran on pins 0.0505" in diameter, a standard reached in the late 18th century but unfortunately a size no drills exist for. In the early days of the 20th century they made drills by filings tool steel wire down, hammering and filing into a spade bit then hardening. In my day we bought HSS drill blanks in exact size then hand ground these into spade drills.
Every working hole was bushed with a felt bush made from a strip of felt glued on one size then formed into a 'U' then rolled up and pushed into the hole.
A very hard process in fact the machines that did this were that secret they were in a locked room and the operators were sworn to secrecy.
|Tony Pratt 1||03/05/2014 17:09:57|
|961 forum posts|
So how is the hole diameter controlled to a "tolerance we can only dream of" in this straight through operation?
|John Stevenson||03/05/2014 17:21:14|
5068 forum posts
Purely by the insert that goes into the spade drill, which in this case is supplied by Mitutoyo to the company.
When they were first approached to make these they were ready to turn the job down because of the specs.
Being basically old school they questioned the tolerances and what was allowable. Mitutoyo looked basically confused and said try this and gave them the drill and when it worked out as it should they were amazed
|Michael Gilligan||03/05/2014 18:01:51|
14624 forum posts
Thanks for the explanation ... much appreciated.
That "Good to Go" process reminds me of when I worked a Kodak in the mid '70s ... They injection-moulded plastic lenses for the little cameras, and the machines took ages to get to exactly the right tmperature and pressure. The operator would run a batch of lenses, which were then checked against masters [to so many fringes]. I particularly remember the "early adoption" of video monitoring for this testing. ... Once the machine was finally stable enough to produce good lenses, they would then run-off a batch of a thousand or more; before anything drifted.
|mick H||03/05/2014 19:54:43|
|703 forum posts|
Graham.....PLEASE write up jig adaptation and method of use for thickheads like me.
|Tony Jeffree||03/05/2014 22:47:13|
370 forum posts
YES please write it up for MEW - and then perhaps one of the suppliers will get these made properly over in China to help everyone out.
|Gordon W||04/05/2014 09:54:06|
|2011 forum posts|
Gray- If it is any help I remember something about the grinding best to be at 90 to the cutting edge. This was many years ago, may have been at tech., but seem to think it was was to reduce the stress fractures on the very edge. All I can remember I'm afraid.
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