View Full Version : how were measurements done?

robert phillips
03-04-2003, 04:14 PM
from a shop semi-newbie

anyone have any good references or tips on homemade measurement tools, angles, straightedge, squares, etc. how did the early machinists/woodworkers design accurate and repeatable measuring tools? what if I want to repeatably measure from about 0.125 to 36.0 quickly with worst case accuracy of 0.005 across the span? would you think physical relationship of turns ratio and belt driven pulley diameters would be good enough? large family with not a lot of bucks to invest in metrology tools.

03-04-2003, 08:28 PM
They did a lot with inside and outside calipers and dividers. Developing the "feel" to use calipers well takes a lot of practice, but apparently if one has the skill, accuracy to a couple thou is routine.

You might want to look up the book, "English and American Tool Builders," by Roe, for some history of how the precision tool industry got started.

As far as what you really need: you don't need a lot of bucks to get what you need to do a lot of shop work. Although I expect it would wear out in a fairly short time, I've seen a 0-1" Chinese-made micrometer with graduations to ten-thousanths for something like $12.50. You can get a cheap (but accurate) 0-6" caliper for under $20. A good 36" ruler with your 0.005" accuracy over the full length will likely cost you the most, but in 25+ years of hobby shop work I've never needed that kind of accuracy for that kind of distance. Maybe you do...but check again.

[This message has been edited by SGW (edited 03-04-2003).]

03-05-2003, 09:55 AM
Accuracy of 5 thou over 36" is a pretty tall order. You're not going to get that even with a high end DRO costing thousands.

Even for repeatability that would be dfficult.

As SGW noted, precision instruments have become extremely affordable. The cheap imports are remarkably accurate and very usable for HSM.


Herb W
03-05-2003, 12:37 PM
Lindsay sells reprints of some neat old tech books...might have something usefull to you. http://www.lindsaybks.com/

03-05-2003, 01:24 PM
Many new DRO scales are glass. Accuracies are down in the microns over a 1 meter (39 inch) length. For example, one of the acu-rite scales is spec'd at either 3 or 5 microns (0.0001") over a 1 meter length.

Mitutoyo has a lower cost DRO based on digital caliper technology and its accuracy is probably around the number that Albert mentioned. You can put together something for the about same price (used or new ebay) with about 10 times the accuracy or better.

If you've got to measure something real long with good accuracy and real low cost, maybe you can have an aluminum (or other metal) rod faced off to a reference length just a bit less than what you need to measure. Then, take a difference reading (with caliper depth rod) between that and your part. You might need to consider temperature effects.


03-05-2003, 07:43 PM
Lindsay books is an excellant website for gear heads. Get a copy of "Modern Tool Making Methods:|" by Franklin D. Jones. It was origianlly published by Industrial Press WAAAAAAAY back in 1915. The things they made and how well they used them will astound you. About $15.00 I think.

Precision measuring tools:
No Money. Small problem. Do what I do. Go to Ebay and bid on the what you need BUT ONLY "off Brands" like Lufkin, Reed Prince, Sherr Tumico, Pratt & Whitney, Etalon (made in Switzerland by Old World watch makers!) etc. Now just bid the lowest bid. Say its $5.00. Ya gotta be there every day and bid first. Set, say, $10.00 as your top bid if you are not first. Stick to it! I got a 0-3" Lufkin depth mic in a wooden case in excellent shape for $5.00 + $3.85 with USPS Priority Mail Flat Rate shipping. $8.85 for a tool that cost $12.00 new but back in 1950. Can't beat that deal! My Etalon 0-1" OD mic listed for $172 and it was a $5.00 special! It takes time and lots of patience though.

Also READ the adds FINE PRINT and look really closely at ALL of the pictures. I got a welding force gage for $2.00. BUT the heart of it was a Starrett 196 back plunger dial indicator in like new condition! Look at what they go for alone! Also don't be shy about Emailing the sellers and asking what else they have that is NOT on Ebay. You may be plesantly surprised at what you can scare up. Cost = Zip, only some of your time! FYI I found my Logan steady rest that way!

The other way is to just go to the area locally that has machine shops, if you have such an area locally, and start asking questions about who has what for sale for how much. You'll be amazed at what you'll find out there! I got my 10" X 24" Logan lathe that way. Took me 4 hours on a spring afternoon to locate it. I just wanted a small 10" or 12" metal lathe, South Bend, Logan, Sheldon, Rockwell, whatever was there and available for the right $$. I got a 1946 Model 200 complete w/a 3/4 HP single phase motor (only needed to plug it in), the original cast steel chip pan, the legs, that great big CI motor holder upper, a three jaw chuck, (only one set of jaws though), a lantern tool post holder, RH, LH, and straight tool bit holders, a new Armstrong knurling tool, a 3/8" Jacobs chuck, a Logan 3-AT collet holder w/adapter and the draw bar (no collets) and a couple of tool bits and a 3MT and 2 MT dead center. Total cost $275 cash American! They even helped me load it in my station wagon.

BTW during that 4 hours I also met a man who knew another guy who had a customer who had two small 6" X 12" TML surface grinders and only needed one and the other one just MIGHT be for sale. When I looked at it it was complete w/a 5" X 10" Brown & Sharpe permanent magnetic chuck. After building back up my cash reserve I got it two months later for $500 and they helped me load it!

Oh yeah, I got my little Rockwell horizontal milling machine by asking my local saw sharpener if he knew of anyone who had a small lathe for sale. Actually I was just trying to find out who had another Logan so I could get some back gears from him. What I found out was that the in rear of his building there was a small machine shop and the owner had just gotten one lot three 13" X 40" lathes from a local school shutting down its machine tool trades courses. He had to take the little Rockwell milling machine or no deal! He didn't want to take it but he had too. I got the mill (new, complete w/gobs of Cosmolene), new 1-1/2HP 3 ph. motor and a new Rockwell power feed all for $150. Hey, those deals are still out there but YOU must find them! Oh yeah, the 13" X 40" lathes (all three fairly new and fully tooled) he wanted $1000 each. I knew that he would take $800 each and maybe less but I had just gotten the Logan and decided to hold off on one. Two of them are still there. Maybe I should stop back and make an offer on one. You interested? We can get a better deal on two! Sorta like a Mini group buy!

You can do the exactly the same thing with precision hand tools. I'll bet you that if you had $100 and two days in a prime machine shop area/environment you could find who had retired, quit the trade, got divorced, needed a drink, whatever and wanted to dump his tools.

I stopped once at a guys house who had a small garden tractor that was free. In converasation with him (as he helped me load it up) I asked him if he knew of a lathe for sale. (Still looking then for those back gears) and he said , "NO but I have two boxes of machinist tools if you are interested". I got an 11 drawer Kennedy tool box and an old S&K Wayne tool box both with some mics, a bunch of end mills, taps, reamers, etc., a 1953 Machinery Handbook, a B&S depth mic, and I can't recall what all else. Total outlay: $25.00 and one simple question.

Oh yeah, you don't need all of the cash up front either. I've worked out a payment plan for heavy ticket items like my welding rigs (I got three, two complete oxy-acetelyne outfits with all of the hoses, gages, tips, tanks (I got 6 Three BIG ones and all had some gas!) the cutting torches and a new Lincoln AC/DC welder w/helmet, optional wheel kit and 25# of assorted welding and brazing rod all for $350.00. Yard sale items from a guy I had never met before! We worked out a payment plan and have since become friends! Nice outcome there. Now thats what I call a real WIN - WIN situation!

Moral of this story: Network like crazy, tell EVERYBODY what you are looking for and have some cash to move on it or at least tie it down when you find what you are looking for!

He who dies with the most toys wins!

Regards, Ken

03-05-2003, 08:33 PM
In answer to your other question as to how to measure from .125" to 36" w/.005" accuracy. Just exactly what do you want to measure any way?

The only way I know is to use a surface plate, height gage, a Jo-block (I got a new Mitutoyo 1.000" grade AA gage block [+.000004"] for $9.00 + $3.85 S&H on Ebay) and a .0001" dial indicator. Set up the Jo-block and get the exact same reading on the height gage then "zero" the dial indicator. The vernier types are now "Old School" and are relatively cheap on Ebay. A 36" one will set you back around $75 to $125+ or so. Bid on "off name brand" ones and see what happens. Oh yeah, you need good light and good eyes (read young) to read the old verniers. An 18" X 24" surface plate will cost $35 to $65+ but the shipping will be rather high depending on just where it's being shipped from. My 0001" indicator (Federal Indicator) was a $10.00 special. This set up will get you + or - .001" across the entire range and keep the Government Inspectors real happy. That is as long as you have traceability and documention on that gage block, dial indicator, height gage, and surface plate all the way back to NIST! Used to be a QC Supervisor in a machine shop that did all DOD, Navy, Air Force and Army contract work. Hope that this helps.


Dave Opincarne
03-05-2003, 09:37 PM
Ken's method is a good one and with the availability of inexpensive gauge blocks and small surface plates (get a decent indicator) you can replicate this setup for no more than a couple of hundred blocks.

One thing though. While useful the height gauge is not needed. If you've got the gauge blocks all you need is a transfer gauge (a stand to securely hold the indicator with the ability to make fine adjustments) to tranfer the measument between the workpiece and the gauge stack.

03-05-2003, 09:38 PM
Am I guessing right that you want the ability to index off parts at precise intervals?If this is the case I have used two pieces of rack gear meshed together to achieve this.This is similar to the idea behind the incra jig system.I regularly used a simple shop made jig to step off box joints that was made from two pieces of althread rod lapped together in place of the gear rack.This method is cheap and althread can be had in a variety of pitches.As for making your own tools I believe Lindsay has some books on the subject also simple hand tools can be made to tight tolerences easier than you might think.I can tell you that tool making boils down to understanding a few pincipals that are logicly derived and elegantly simple in concept.Once you begin to think in these terms and understand the thought process anything is possible.

03-05-2003, 10:03 PM
I find it really objectionable when companies like Acu-rite will actually claim accuracy of 5 microns over a meter. This is the thermocoefficient of pyrex Steel will expand by 13 microns over a meter with a change of 1 degree celcius! Who's kidding who.


03-06-2003, 12:23 AM
You are absolutely right about the effect of temperature. I think Acu-rite and others spec the accuracy at 20 deg. C. Heidenhain uses Diadur glass and the temp coefficient is 8ppm/deg.K. This would give 8 microns per meter per degree.

If a shop ranged from 60 degrees in the winter and 90 in the summer, that would give a 240 micron (0.009") error per meter.

DROs which have a "scale factor" would allow you to compensate if you took temp and specs into account. Maybe high end DROs compensate for temp as an option ??

03-06-2003, 08:34 AM
Acu-Rite and others are claiming their scales are built to that accuracy, and I have no reason to doubt it. That's NOT the same thing as the accuracy you may be able to get out of them.

High-end DROs offer "linear error compensation" though, so you can measure and compensate for error of the DRO on your machine, in your shop. Of course, the correction factor you apply will be only as good as your ability to measure more accurately than the DRO. It would have to be done with gage blocks.

robert phillips
03-06-2003, 10:31 AM
thanx to all of you for your insight and taking time to answer these questions. i sent for a lindsay catalog. also berg, stock drive products, and others. my main interest is in homemade positioning systems and hence the desire to get all the way out to 36 somewhat reliably. but can't check the initial positional capability without decent mechanical standards (to me decent means like used/surplus gage blocks, steel rules/squares, angles and so on -- not cmm or things like that.) i would really like to hit +/-10 mils on the position but to verify position i would need a range of measures to get me out to 36. i'm hoping that fixed mechanical relationships (gear, cog belt, pulley etc) can keep me in an acceptable range once i have the ability to measure where i am. i like the allthread idea but how consistent would threads be across 36" span (if used as a lead screw)? especially, i'm sure i will need a parallel drive setup, so now there are two parallel drive screws just like the x axis only of an xy carriage. this will be challenging and fun, but probably pretty frustrating too. a shaft encoder will get me repeatability along with a little software to control the motor to account for backlash. all of your experience with lathe tool positioning drives probably gives you all a good feel for ability to position to a given spot.

03-06-2003, 10:37 AM
Linear error compensation is supposed to correct for errors in the machine bed / tool. I suppose that feature could be used correct for self-induced errors if a mechanically based DRO starts to wear in some areas. In either case, you'd have to do some careful measurements on your machine to see where it's off.

The lower end Acu-rites allow something like 3 bands of correction. I think I've seen others offering 99 "bands". They do claim the accuracy specified and it is at 20 degrees C.

Imaging technology can get down into the low nanometers (resolution) but I think verification is where the question lies.

At these claimed accuracies, they probably use some sort of interferometer for light/wavelength based measurement.

I still haven't figured out how to mount the darned things on smaller machines.


[This message has been edited by nheng (edited 03-06-2003).]

03-07-2003, 02:08 AM
To get glass scales for my Maximat 7 and still allow full utility is extremely expensive - the small size of the machine is a definate disadvantage. High Accuracy glass scales run about $500-$600 CDN for up to about 60". No real price break for a shorter module. It just as expensive to use an electronic indicator (Sylvac, Starrett, Mitutoyo) and readout than to try and mount normal scales. The electronic indicator is the size of a pen with a cable.

03-07-2003, 10:00 AM

Glad you're back and hope you're feeling better.

I got lucky and picked up three glass Heidenhains, brand new, TTL output, from an ebay guy (outside contact) for about $100 each. A sweet 120mm and also a 320mm which should handle my carriage needs (and a 220mm spare). They are the LS473 (LS series, funny number for specific customer) and are +/- 5 micron accuracy !

Just had to wire to a 9 pin for my acu-rite turning dro. The scale housing is about 18mm thick X 31mm tall (see that, metric info for you CAs http://bbs.homeshopmachinist.net//smile.gif ). What's the series of the Mitutoyo indicator stick ?

Email me if you want the contact info for the scale guy (he may still have some).


[This message has been edited by nheng (edited 03-07-2003).]

03-07-2003, 10:32 AM
I've been lucky anything I've wanted I've found at yard sales and on ebay. I go with the name brands like Starrett or others. I'm hearing that machine shops are going out of business (some to retirement) in record numbers, you'd think they was a telecomm parts manufacturer. I'd be checking around the local shops they'll know who is retiring etc. I've seen a lot of machinist retiring and just putting their whole tool box up for sale you have to take the whole thing good with the bad. Buy the whole box is you can afford it and put the rest on ebay. Might make your money back that way. You might want to read "Fundamentals of Dimensional metrology" published by Delmar Publishing isbn 0827301936. I'd look for that book at www.abe.com (http://www.abe.com) and get it used.
If you want to go optical (interferometer) then you might want the dover book "Studies in Optics" by A.A. Michelson ISBN 0486687007. Michelson is considered by me to be one of the kings of Metrology.
Good luck with your project.