Turning to a diameter

[doubleboost]

Hi

Sand paper is for cabinet makers
Engineers use emery tape :big: :big: :big: :big: :big:
John

 

[lensman57]

Hi

Sand paper is for cabinet makers
Engineers use emery tape :big: :big: :big: :big: :big:
John

I stand corrected, it is emery cloth as you say.

Regards,

A.G

 

[tel]

turning to a diameter is easy - turning to a given diameter can be a bit harder.

Wot Marv said tho - for work that matters, lose the abrasives and learn to use the tools.

 

[rake60]

When I was working in a job shop, bearing fits were a common requirement.
Diameters averaged the 14" range for industrial applications.
+.0005 -.0000 are the standard tolerances.

I don't know of many manual machinists who would cut to split that half thousandth tolerance.
We cut toward the low end on a bore and high end on a shaft, then polished the size
to finish with emery cloth.

Cutting for a finish size in a hobby shop is fun.

When your income depends on hitting that size every time, you learn to use emery cloth.
Try scrapping a couple Caterpillar D9 hubs at work. You'll be looking for a new career soon.

I do not miss that daily pressure!

Rick

 

[digiex-chris]

Sandpapering is fine on decorative items and anything where you don't care if the part is truly cylindrical but if you want something really cylindrical, like a piston for a piston valve, lose the sandpaper and learn to turn to size.

Or make a cylindrical lap for when you need the nice surface finish and an exact size. Very common in fitting a lapped piston to a bore. There's a certain luxury to not having to have it done NOW.

I found my Taig dead on. Didn't have many problems with it. I still use it for really, really small stuff. If you're using the compound, don't. Only use it if you need an angle.

 

[Mike N]

In Tech school we called it "Flexible Finishing Tool" (emery cloth)

 

[chrsbrbnk]

since all machines spring ...the standard tech book method is to take the last 3 cuts the same amount say .1 to go three cuts of .033 and making the small adjustement this also keeps away the problem of a rough cut with too small a cut say like trying to take .0015 on the last pass with a carbide keeping in mind to allow the work to cool before the last three passes

 

[sunworksco]

Should a machinist use a stick to hold the emery clothe as to not get wrapped up in the lathe?

 

[n4zou]

The lathe is not going to grab you unless your wearing long hair, loose clothing, or long sleeves.
Here is how you do it.

Filing and Polishing on the Lathe
http://www.smithy.com/machining-handbook/chapter-3/page/32

 

[Sshire]

Thanks again. I used many of the suggestions, lots of spring passes, miked after each pass, came up with this. Happy guy! ;D ;D ;D

Best
Stan

 

[steamer]

Sandpapering is fine on decorative items and anything where you don't care if the part is truly cylindrical but if you want something really cylindrical, like a piston for a piston valve, lose the sandpaper and learn to turn to size.

What Marv said.

You can turn the compound to approximately 6 degrees ( OK 5.73 degrees) from the axis of the work and then the dial on the compound will then advance the tool into the work by .0001" per thousandths on the dial.

But don't kid yourself. The tool has to be razor sharp to do this....especially with a light lathe.

Dave

 

[mgbrv8]

When I strat getting close to my critical dementions I like to start feeding both directions. For example cut in feed in towards the part once to my stopping point reverse my feed a feed out without feeding in any more. To cut this will take what ever small spring back you have. And really helps you to sneak up on a demention. Also if you have removed a lot of material make sure to cool your part thoroughly while your still .010" or so away so you allow the part to grow back to room temp before you do your finish cut.

 

[chrsbrbnk]

Actually a lathe will grab on to emery paper really well! SO if your holding the emery paper in both hands with say a 90 deg bend around work your pretty safe but close the angle up to where the emery paper ends touch each other even the slightest slack will wrap that paper at just amazing speed if your lucky it'll suck out of your fingers if not just use your imagination.
Anyway laying it on a stick or a file gives a lot flatter surface as opposed to football shaped

 

[Runner]

Hi Stan,

you have put to good use many of the tips that have been posted in reply to your query, hence you are happy at being able to achieve a diameter of 0.37500". I suspect that the drawing didn't require accuracy to 5 decimal places, something much less. Anyhow the Starrett Electronic Micrometer has an accuracy of +- 0.0001", which is very good, but less than the resolution provided by the LCD display. The electronics introduced to measuring instruments have enabled the resolution to be increased, however the accuracy is still dependent on the mechanical items that make up the micrometer. I hope that you don't mind me raising this, I think posting the picture you were providing the greatest visual impact and having a LCD display reading of say 0.37501, although would be more than acceptable, would slightly loose its impact on the reader. It's good salesmanship.

I also have learned a great deal from your post, thanks for raising it.

Brian

 

[Sshire]

Brian
At this point in my journey to learn how to do this stuff, I'm happy to hit +- a thou. I'm quite sure that most of Elmer's engines would allow that.
That said, after reading the hints and techniques that everyone posted to my question and trying them, I was so excited to get that reading on the mike, that I had to take a picture. Probably couldn't do it again to that many decimal places.
My goal now is to try to get the diameter to as much accuracy as I can. It's what you might call a "character building exercise."

Best
Stan

 

[Blogwitch]

Stan,

Please don't fall into the precision trap.
You will find you will spend more time trying to reach the almost impossible size, rather than concentrating on getting the part made.

In industry, or when doing work for others that requires such low tolerances, then fine, go for it. But for normal home workshop work, it just isn't necessary.

I used to aim for tenths when my shop was set up as a precision machining shop, but now, almost everything I make, is made to a thou accuracy, or even a couple of thou sometimes, all depending on what I am making.

Your time would be better spent trying to learn 'quickfix' problems you will eventually encounter, like where you have to make a turned part 'grow' a couple of thou, to give you a nice interference fit.
These things will be a lot more useful to you later rather than searching for supreme accuracy.


John

 

[Sshire]

John
I agree wholeheartedly. I just came up from the shop after turning a ship for a Thum Engine for my great nephews birthday gift. It was to be 5/16". Took me an hour as I was looking for a sliding fit in a bearing.
I'm sure I'll get faster. Didn't want a sloppy fit but, of course it had to turn freely. Very small difference between the two fits. I am having a good time doing it

Thanks for all of the advice. More is welcome.
Best
Stan

 

[Ken I]

Even when turning or milling non-critical dimensions I try to get it spot on every time - call it pride or ego but I'm always pleased when something mikes up spot on.

Besides its good practice in getting to grips with the vargaries of your machinery and materials that it makes it that much easier to do when it counts.

You have to hit size on the last cut - if you find you are 0.0005" oversize, its time for the emery paper - a cutting tool is likely to simply ride off and do nothing or dig in and remove more than you want. you generally can't dial in such a small increment (depending on your machine and materials being machined) other than on a grinder.

Ken