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16th Oct 2013, 10:33 PM #1Golden Member
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+/- 0.002mm 25mm cylinder 100mm long - reading between micrometer lines ?
Hello,
See attached scan of page from Harold Halls book "Metal Lathe for Home Machinists" Chapell Publishing Company 2012.
Does this imply that I should be able to cut a 25mm cylinder 100mm long +/- 0.002mm on the diameter ?
My micrometers can comfortably measure xx.00mm but not xx.002mm.
Do experienced people estimate the third decimal place when using micrometers ?
When I think I am measuring 25.00mm am I really somewhere in between 25.00x and 24.99y ?
Thought I was doing pretty well to get it within 0.01mm between top and base of cylinder (and it was the dreaded black bar ... achieving a better finish now) - had a go with shims prior to trying jacking bolts and got lucky on the 2nd shim. Finding it hard to believe that young Harold expects me to do better ...................
I really didn't believe the bed could be so far out - levelled with builders level first - then did the cylinder test - 0.92mm with 2 shims - is that excessive ?
Can see that trying to get that last 0.01mm with shims would be a painful job - would be using Alfoil shims - will try bolts tomorrow.
On another note have been reading "The Amateurs Lathe" by Sparey and "Using the small Lathe" by L C Mason - I think they are great, written a long time ago, sometimes they have a brilliant turn of phrase - one of them discusses how he made a home made parting tool from a hacksaw blade. Both books available from Victorian public libraries.
BillLast edited by steamingbill; 16th Oct 2013 at 10:52 PM. Reason: replaced 25.00 with xx.00 - attached scan
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16th Oct 2013, 10:45 PM #2
Hi Bill,
Harolds books are mostly very good. But the tolerances he talks about there are a bit crazy. Certainly better than i get from either of my (working) lathes. With that Tesa mic you should easily be able to read .005mm, ie half way between the lines. Maybe even .0025mm. But if you can get the lathe cutting to .01mm in 100mm that is darn excellent. Any better than that and you start facing all sorts of problems, mostly in your case with repeatability with what is a lighter lathe.
Some mics do have a vernier micron scale, but i always take the reading with a grain of salt, since without a constant temperature environment it is pretty well meaningless.
On that though you need to make sure your work piece is not getting too warm at one and, most likely the one without the heatsink (chuck) hanging off it.
Cheers,
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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16th Oct 2013, 10:55 PM #3
books
Hi
I have read most of Harolds workshop series booklets . From a beginners perspective, he explains things pretty well and his projects are excellent . But, he can go off on a tangent and waffle on about things that are really of little use in a hobby workshop . As an example, I read his piece on fitting a new lathe chuck backplate to its spindle register ... he went on and on about how vital it is to have the diameter of the lathe register spindle , within a minute fraction , match the chuck that was to be fitted .
If you look at his workshop, he only uses basic machines . A Myford lathe and a small mill drill . I don't know how he measures things but he seems to use only basic run of the mill dial gauges .... Mike
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16th Oct 2013, 11:24 PM #4Most Valued Member
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As Ewan says, some 25mm mics come with a vernier for 0.001mm.
Now as he also says you arent going to be able to measure that good in the absolute sense. But you dont care about that only repeatability, so knock yourself out and read between the lines
Which is the big end?
Do you have a DTI?
What tool are you using?
Stuart
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17th Oct 2013, 07:39 AM #5Golden Member
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17th Oct 2013, 10:21 AM #6Most Valued Member
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Well thats a start.
Not exactly, but it may have been able to display where some of your error was. Now given that you are using HSS and its big the chuck end, hopefully deflection isnt much of an issue. Though you can use the DTI to check. set it up at centre height and run it aong the side of the bar.
I'm not sure what you mean. you adjusted the lathe with 2 shims totaling 0.92mm? or you had an error of 0.92mm on your cylinder?
I've no idea how good(bad) builders levels are. And here is the problem with setting lathes up withoout a good level. You have to assume the headstock is correct(which hopefully it is)
0.01
Sure, on my Mitutoyo mic(is it goes to 0.001mm) I can say that the lines are about 0.001mm wide*. so if opposite edges of the lines are touching thats 0.001mm, if there is a gap about the width of a line thats about 0.002mm and so on. If you practice on the same spot on the bar to see just how careful you need to be to get repeatable readings at that level and move to the other end of the bar.
(this shouldnt be confused with being able to measure the absolute size of soemthing to the nearest micron, you're just comparing one end to the other)
If the lines line up your on 25mm +/- 0.001mm.........how that relates to an absolute measurement is anyone's guess
Having said all that, given that you big the chuck end, unless you have something special in mind I'm with Ewan and would be thinking about calling it good.
Enjoy your trip to the tool capital.
Wait did I just call myself a tool?
Stuart
*well ok the lines aren't 0.001mm wide but they represent 0.001mm
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17th Oct 2013, 11:03 AM #7Golden Member
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17th Oct 2013, 04:26 PM #8Most Valued Member
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leveling
hi mate ive recently been thue this myself.
i was using a imperial mic and ended up buying
a metric one so i didnt have to read in between
the lines.
i didn't want to use 25mm bar because i thought it might flex
and went for 49mm bar instead.
what sort of lathe do you have? what cutting tool were you using?
and what was your depth of cut.
i think to start with a standard o.o1 type mic will be more than
accurate enough.
do you have a camera to show photos of your lathe ect?
aaron
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17th Oct 2013, 05:20 PM #9Most Valued Member
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Don"t go chasing unrealistic figures in the backyard too much.
From what i have read you don't have a great deal of experience,just try and get your work to within .001 to .oo2" over your short length of material.
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17th Oct 2013, 06:21 PM #10Golden Member
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Yep
Thanks for all of the responses.
Pipeclay, that is an understatement - I have no experience - hence the initial post looking for a reality check from you folk on that 0.002mm - I was terribly peeved when I compared that to what I had achieved.
I don't feel so disappointed now. Actually quite chuffed.
Will leave things exactly as they are until I better understand what I can and cannot expect to be able to do.
To answer some of the points raised above - Hercus 9" model A lathe, initially levelled with a carpenters level, then the 100mm cylinder test resulted in 0.92mm of shims beneath the back of the tail end, (0.92 shims - does make me wonder about my carpenters level) final finish on cylinder was .001" cuts done with knife tool, see attached sketch from "Using the Small Lathe" by L C Mason. This currently gives me smoother finish than my finishing tool - learning how to sharpen that is probably next thing I try - Have got the Workshop Practice Sharpening book by ............ Harold Hall - he wrote lotsa books.
Thanks again
Regards
BillLast edited by steamingbill; 17th Oct 2013 at 06:25 PM. Reason: forgot attachment
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17th Oct 2013, 10:55 PM #11Most Valued Member
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well done
hi mate 9"a lucky you. that's a good machine. do you have the hercus manual
i think its called something like a guide to turning.
0.01 mm taper is a real good start.
good luck with your machine
aaron