Metric to imperial

Hi all

I have a Denford Viceroy with metric leadscrews and graduations of 0.025.

I work with metric drawings but my stumbling block is knowing quickly how much cut is needed to get to size without reaching for the calculator.

For instance, say there is 0.73mm to come off halve it 0.365 (thats the easy bit) how do you know quickly how many 0.025's there are in it.

Regards

Your starting clue 10 = 0.25

Well, obviously there are at least ten of them, so let's start with that.

Now there is 0.165 left over, which is 0.050 x 3 so it's 0.025 times six, plus a bit left over. The bit left over is less than the increment of .025 so that's probably as near as you're going to get it in one go.

Answer is 16 and a bit.

The remainder is 0.015 or about half a division. I'm not familiar with the machine; is half a division resolvable?

Hopefully the principle of successive deduction works OK for other starting points.

Make things easy on yourself by simplifying the arithmetic, You could try treating each division as 0.05 mm off of the diameter. That way, you are dividing 73 by 5 instead of 365/25.

As it is even easier to work in tens, you could do the calculation quicker if you double the amount you want off of the diameter and shift the decimal one place.

73 x 2 = 146

shift the decimal one place to get 14.6

Take of 14 1/2 divisions.

Brian G

Edit.  If you are happier with imperial you could switch to thou for a sense check.  0.73 x 40 is just under 30 thou, each division is about 1 thou (or 2 thou off of the diameter), so you are looking to move just under 15 divisions.

Edited By Brian G on 05/01/2021 22:54:38

How about fitting a DRO? That way you can work in metric/imperial and by radius or diameter

Martin.

..or a slide rule

.. or just draw a graph and laminate it

..modern folk use the calculator on their phone...

pgk

Removed post, I didn't read the post correctly.

Emgee

Edited By Emgee on 05/01/2021 23:05:34

I've just realised why I can't ever seem to make something to size.........

It's simpler to do the maths in ones head the other way round given that 4x0.025 = 0.1mm. So for 0.73 it's:

7x4 remainder 0.03, call it 28 remainder 0.025 = 29

divide by 2 gives 14.5

Exact answer is 14.6 but that's only 2.5 microns difference on the dial. Of course it also depends if the cross slide dial measures radius or diameter.

Andrew

Probably confusing but i'd say 4 off 0.025 is .1. So then there are 4x3 divisions to get the 0.3 done leaving 0.075.Then another two divisions cover 0.05 off that leaving 0.015 which is a "tad" or part division.

I got fed up with the mental gymnastics and made a new set of leadscrew collars with 0.02mm graduations! (Chinese mini lathe)

I made new collars because I wanted to make them re-settable / lockable, but you could just make up graduated sleeves to slip over the existing dials if you're happy with them otherwise.

The collars were made from aluminium. Graduations were made using a boring bar on its side and a pointed HSS tool; Indexing with a printed pattern glued to an extension on the spindle and numbers using a punch. I did anodise them afterwards and they're holding up well.

Short term pain for long term gain.

The remaining bug-bear is the 1.25mm pitch cross slide leadscrew. I can see me replacing it with a 1mm pitch one sometime.

Edited By Andy_G on 05/01/2021 23:52:23

I would re-make the dials with 250 (or 125) graduations and save my brain from hurting.

Just multiply the 0.73 by 20 (there's no need to halve the 0.73)

0.73 x 20 = 14.6

If you are doing the x20 in your head then split it into two parts. 

(A) shift the decimal point to multiply by ten.   (B) double the answer.

In your example this would be   0.73 becomes 7.3  (that's the x10 bit)  and double that is 14.6

Just to show it works, there's no need to do the next bit.

14.6 increments at 0.025 each = 14.6 x 0.025 = 0.365 which is the depth of cut you are looking for to take 0.73 off the diameter.

Regards

Steve

Edited By steve de24 on 06/01/2021 00:28:46

Sorry to venture off topic, but Andy, could I ask, did you anodise with a home kit? I made a post a while back about a cold blackening kit that worked really well, and haven't tried anodising, but if that was achieved with a home kit it might be worth having a go, it looks very good.

Thankyou! Yes, it was done at home. I have been amazed at how well it works myself.

It basically follows the process i this video:

https://youtu.be/Z1zT8p7d9Z0

PM me if you want more details, or we can start a new thread.

Thanks for reply Andy, might be worth starting a thread incase others are interested.

Hi Athur, as mentioned previously

Best option is to fit a DRO and you can read in either imperial or metric. (And remove the problem of calculating for back lash).

A cheaper option is to fit a digital caliper or dial indicator. Lots of examples on Youtube of how to do it.

A high tech, hands free option is to get one of those new  electronic deviices that does everything by voice command and say "Hey Google, what is 0.37mm in inches"

A simple option (if you don't want to use a calculator) is to print a table of converted measurements from inches to mm and keep next to the machine. (like that shown below) Lots more on the internet.

**LINK**

Your example of a conversion for 0.73mm (0.737mm = 29 thou)

Paul

Edited By Paul Lousick on 06/01/2021 04:29:51

how do you know quickly how many 0.025's there are in it.

Divide the number by 0.025.

Same as if you divide 1 by 0.5 (the answer is 2 (halves) , unsurprisingly). Exactly the same procedure for any numbers you can think of.

.

Or, for much simpler mental arithmetic ...
[ which was, I think, the essence of the opening question ]

Multiply the number by 40

For example: 

... As previously suggested by Steve.

.

MichaelG.

Edited By Michael Gilligan on 06/01/2021 08:42:49

Am I missing something here. Everyone is giving a load of calculations. Why not just divide 0.365 by 0.025. simples.