Converting drawings

[John Lee]

alanstepney said:

One advantage of Imperial is that there are vast amounts of tooling around, and much can be had for a pittance.
The numbers of drills, threading tackle, reamers etc that I have found at, for example car boot sales, is amazing.
OK, you can pay out a lot of money if, (a) you have it and (b) dont have better uses for it, but there are bargains to be had, more often with what isnt popular as it isnt used in industry.

Exactly Alan,

End and Slot Mills for example, and Woodruff Cutters, Slit saws, you name it. You can buy a £4 or £5 each off Ebay, or more at you local ME sellers or.......

Here is my sorted out collection, both metric and imperial:



And here is a box full that I might sort out if I wear those out:



£50 at an auction of a failed engineering company's assets.

Count if you will, about 1000 in total. They will see me out...

Regards,

John

Ohh..by the way, the syringe and needle is full of oil, before anybody comments..the ideal accessory for the ME. I may auction it on ebay ;D

[gugger]

"The limitations of metric (threads) are that there isnt just one standard, but several.
Additionally, there isnt the option of "size smaller" and hence more accurate to scale, heads and nuts."

Despite beeing very familiar with the Imperial and Metric system and with the various threads in both systems I can not understand the above sentence. Can somebody explain to me what the different standards in metric threads are?

[paul]

£50 at an auction of a failed engineering company's assets.

Count if you will, about 1000 in total. They will see me out...

Sounds like a fantastic deal - trouble is buying stuff like that with no experience could land you a pig in a poke (or 1000 pigs in this case) unless they were new.

[havoc]

Despite beeing very familiar with the Imperial and Metric system and with the various threads in both systems I can not understand the above sentence. Can somebody explain to me what the different standards in metric threads are?

Not very sure myself, but I think he alludes to the fact that for a given diameter of fastner there are several possible pitches. Like M12, the normal one is M12x1. But you can just as well specify M12x0.5, M12x.075, M12x1.25, M12x1.5 or M12x1.75. On the other hand you will have to look very hard to find anything else than M12x1 or M12x0.5, even the latter being not easy at all. The thing is however that this are not different standards! It are all different threads defined by the same standard for different purposes. (M10 and M12 are the worst in this aspect, most have a single pitch or 3 pitches: normal, fine and coarse)

What he means by a size smaller is that in metric the size of the head of a bolt is fixed in relation to the diameter. So a M3 isn't a 1:4 scale M12.

[S.D.L.]

The baseplate holes I made 3mm because - beginner's workshop zone - my drills are in 0.50 steps. I put the 4 corner holes at 5mm rather than 4.75mm 'cos it's easier to measure and puts them fractionally more inboard but they won't foul anything.

As a start get a set of 0-6mm drills in 0.1mm steps good quality drills will be cheaper than number drills and can be used as tapping sizes for metric or imperial. I use my 0-12 by 0.5mm drills for gereralclearance holes and save the .1mm step set for tapping ho;es etc.

If you want top quality try these

www.greenwood-tools.co.uk/ishop/728/shopscr75.html

If you want a more budget range try here.

www.jlindustrial.co.uk/cgi/insrhm

and search drill set there is various price selections of 1-5.9 by 0.1



There is no reason that you cant make nuts any size to suit the thread, get the hex size you want drill tap, and part.

There is more people working metriac as time goes on. They stopped teaching using imperial in 1968 when i startted secondarey school.

Steve Larner

[alanstepney]

There is the common metric coarse, a metric fine and extra fine (some sizes only) and 3 or 4 fixed pitch across all sizes.
In fact, there is at least as much variety as we had with Whitworth. (BSW.BSF, BSB, BSP, etc)

As for cheap tools, last year I picked up a large box of drills, taps and "funny things like drills but straight" (I call 'em reamers, but FTBS describes them OK!) for the princely sum of £5.
Worked out at under 5p each, although I was having to pay 10p each for drills at a local car boot sale. Not too bad as some were over 1/2" and a few 1"+.

However, I also bought a set of drills from Northern Tools (a search will find them) comprising 1-60, letter, fractional and metric, 120 (or so) drills for £46.
I wondered if they would be rubbish, but somewhat to my surprise, they are excellent.

[gugger]

I got a bit annoyed by the remark that there are different standards in Metric threads, which is not correct. There is only one standard. What you find in Metric is different pitches exactly as you find it with the Whitworth treads.

For model engineering you have up to a size ½” in Whitworth basically 12,14,16,18, 20, 24, T.P.I in addition you have the ME Threads with 26, 32, 40 T.P.I.

In the metric system we do not count the pitches in an inch, but the pitch distance in mm.

The normally sold and used 12mm thread i.e. M12 has a pitch of 1.75 going to fine thread for M12 you will find 1.5, 1.0.

The normally sold and used 10mm thread i.e. M10 has a pitch of 1.5 going to fine thread for M10 you will find 1.0, 0.75.

The metric taps that I have and mostly used in model engineering during the last 30 years are:

Common or
normally sold Fine thread
M3 0.5
M4 0.7 0.5
M5 0.8 0.5
M6 1.0 0.75 0.5
M7 0.75
M8 1.25 1.0 0.75
M10 1.5 0.75

Below 3mm I have the dies and taps from 2.6mm right down to 1mm. For this sizes BA can be used.

The size of the bolt heads is of no significance since they have to be sized down to look right on the model anyway.

Over the years I have seen a lot of misleading information about the metric system. Maybe this information helps a bit concerning threads.

Walter

[alanstepney]

OK, let me correct my statement.
There is one metric standard, but several dfferent pitches for each diameter.

That is no different from Whitworth where there are BSW/BSF etc where, once again, you have diferent pitches for each diameter.
Exactly as with Metric, there is ONE standard, which is 55 degree angle etc. etc.
The same applies to BSP, ME and others which are, again, to Whitworth standards.

One of the big "selling points" of metric was that it would reduce the variety of taps and dies we would need.
That hasnt happened, nor will it due to the variety of pitches that are available in metric.

Of course, whether using metric or Imperial, one rarely needs all or even most, of them.
The answer is to get the most common, plus what you need when you need it.

Now, when you move on to BA then it all changes again!

[gugger]

Alan,
Your statement has been accepted.
I will not comment “selling points”. A fact is that in industry and in our activity various pitches are needed and have to be available, no matter if the Imperial or Metric system is used.

Walter

[John Lee]

paul said:

£50 at an auction of a failed engineering company's assets.

Count if you will, about 1000 in total. They will see me out...

Sounds like a fantastic deal - trouble is buying stuff like that with no experience could land you a pig in a poke (or 1000 pigs in this case) unless they were new.

Not really Paul, they were 95% new, still in the little red boxes you see with my spares, still in their hard wax protective coatings.

This is how the hardcore ebayers are getting them sometimes, and then selling them on at huge profit. If it was not for the fact that I can use them, I might well do the same ;D

Just trying to deflect away the metric debate that starts again.. But ... I can't help it . If you want to buy new, £50 or so will buy you a full set of metric drills (cased up) in 0.1mm increments up to 10mm. You can substitute for any number, letter or fractional drill. For the minute difference in sizes, drills are inaccurate devices anyway, does it matter??

Regards,

John

[steammadman]

Can't see the problem,with a digi caliper the reading comes up in the window,
start in imp, press mm, and hey presto the EXACT conversion comes up.
WHAT CAN BE EASIER ?

[Myford Matt]

Very good point JL and one I have often wondered about. Using a 0.1mm step set of good drills you will never be more than 1000 x 0.5 x 0.1 / 25.4 = 2 thou away from any size. How accurate is a good set of Dormer bits?

If you drill 3/16" carefully, everything bolted down and use a good quality, well-maintained pillar drill with cutting fluid, what is the expected range of diameters? Would it really matter if you used 4.8mm, which is just under a thou bigger.

I suppose what I am asking is at what point do you say I need to machine a diameter more accurately than a good quality, properly used drill bit?

MM

[Myford Matt]

I know it's irritating to ask a question and then answer it, but I phoned Dormer via Greenwood tools and they (Dormer) were most helpful. For the kind of drill bits we normally use, say the 202/203 sets available from Greenwood, they are classified as general purpose H12 tolerance. This means that in the following ranges there is a POSITIVE tolerance of:

To 3mm; +0.1mm (4 thou)
3-6mm; +0.12mm (4.75 thou)
6-10mm; +0.15mm (6 thou)
10-18mm; +0.18mm (7 thou)
18-30mm; +0.21mm (8 thou)

The tolerance is strictly positive because the error does not come from grinding the drill bit (that is very accurate), but the inherent nature and operation of a drill bit – obviously it won't drill smaller than the (accurate) diameter of the bit, but it will be deflected as it drills down (depending on depth, material...). I suspect Dormer are being conservative, but it shows why the range is 0.1mm, there’s simply no point in finer ranges because they would be swamped by the tolerance.

They also pointed out that reamers are at least ten times more accurate (made to H7 tolerance).

Dormer do make more accurate drill bits: ADX with special geometry and CDX (carbide), but they are at least five times more expensive.

I guess the upshot of this is that all you need is a full set of good 0.1mm step drill bits and you will easily be able to drill imperial, number and letter holes within the tolerance of equivalent bits.

MM

[alanstepney]

As a slight digression, last year I bought a "cheapy" set of assorted drills from Northern Tools.
Number, letter, fractional and metric, all in a nice tin case, for under £50.
I half expected them to be total rubbish, but to my pleasure, they are excellent.

(Didnt really need all of them but I had a credit note to use up!)

I see that the same set is no longer listed, although similar ones but TIN coated are, at a higher price of course.

Given the tolerances that Myford Matt mentioned, I wonder how many of that set are duplicates?

[ron]

Alan
I bought the same set from Screwfix a couple of years ago for about the same price, but I don't think they list them now either, they are pretty good value for money but I did have one that completely shattered, it looked as if they had forgotten to temper it?


As a slight aside, I was reading a ME from 1978 and the following was written in the text of a design,
'I am sure it will not have gone un-noticed that both imperial and metric dimensions have been used in the drawing/text. In a few years time we will be 100% metric and at least consistent'
Yeah right ;D

Ron

[John Lee]

myfordmatt said:

Very good point JL and one I have often wondered about. Using a 0.1mm step set of good drills you will never be more than 1000 x 0.5 x 0.1 / 25.4 = 2 thou away from any size. How accurate is a good set of Dormer bits?

If you drill 3/16" carefully, everything bolted down and use a good quality, well-maintained pillar drill with cutting fluid, what is the expected range of diameters? Would it really matter if you used 4.8mm, which is just under a thou bigger.

I suppose what I am asking is at what point do you say I need to machine a diameter more accurately than a good quality, properly used drill bit?

MM

As you say, you answered yourself Matt. I bought the full metric set some years back. I bust a few, usually the 3mm so I just replace those. I cannot really see the need for more, or indeed more complication. Tapping and clearance sizes for all the imperial threads are available in metric.

To answer your last; drills do not make round holes. They make 3 lobed holes. It's only at this point (bores for pistons, pins for motion linkages etc etc) you need to machine, or lap, or ream a diameter more accurately. Certainly not a consideration for clearance holes or tapping.

Regards,

John