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retaining position locations on mill without DRO- vernier scales, stops, ?

stoneaxe

Stainless
Joined
Mar 2, 2010
Location
pacific northwest
Seems most mills these days have a DRO. Let's talk about the old days:)

When a series of features are called out, and referenced by location to a zero point, either by absolute or incremental, it seems very easy to lose track of rotations on the dial. If a miscount is made, the .200" of a rotation is hard to pick up visually. Also, if a error is suspected, how would one know where the zero point is, in order to return to it for a double check?

Mechanically, I see two ways to help with this. A simple vernier scale on the tables, so a rough check to the nearest .200" would be easy, or an adjustable mechanical stop to limit table travel. This would be set at a zero point.

Or a piece of tape stuck on the table with a pencil line..!

Is a mechanical stop like this a bad idea? The problem is that if it is forgotten and used with the power feed it will trash the mill. I see them used on manual lathes, but perhaps the feed clutch is designed to protect in this situation.

Can some of you old pros enlighten me as to how to retain position?
 
If it is a relatively simple/cheap part double check with a tape measure, If it is a complicated/expensive part break out the blueing and lay the feature locations out.
 
All you need is common sense. Let’s talk a milling machine. Common one with a table. You can crank it all the way to the ends of X travel, then note or memorize the number of turns of the crank for a certain X point. Same on Y and Z.

You can establish an XY center by aligning a table chuck by the spindle, mechanically by a ground cylinder in collet in holder in spindle. Once you have that you put a mark on the X and Y scales with a permanent felt pen, zero both vernier wheels, now you can’t get lost.

Z is zeroed by an intermediary height setting gauge. Mostly you have two-inch ones, in Europe 50 mm.

Another reference system is the machine table. Relative to its edges you can establish a grid, purely mechanically by pushing a parallel pad against a table side and aligning something by it. That way you can locate a vice on the table, if necessary by the aid of gauge blocks. You can locate something relative to the vice’s ground jaw(s). You can install a stop, fastened in a T groove of table or mounting block of a shaper. A little imagination makes the difference between a fool machinist and a cool machinist.
 
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backlash and leadscrews not being that accurate plus temperature changes and literally some machine tables sagging under weight of heavy part. you literally cannot hold .0001" tolerances based on machine locations cause machine changes based on backlash, temperature machine sagging and many other factors
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also literally i see often, turn coolant on and one end of a large part can easily change over .0003" from temperature differences. and Tram error or spindle leaning basically longer length tools tip center is out of position compared to shorter length tools. visualize spindle leaning 45 degrees as tool gets longer its tip center goes further in the direction of the spindle lean. everyday i can bore a hole with a short boring bar, replace boring bar with indicator in the spindle and if indicator setup is longer it will say bore just done is out of position. it can easily say more than a .0002" error
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that is also reason why even with a DRO what DRO says is often not true. also DRO calibration being checked with gage blocks almost all show DRO error. some DRO have a calibration mode, if you move 10.0000 and its says 9.9998 you can calibrate it so it reads 10.0000 with 10.0000 movement. cheaper DRO sometimes dont have this calibration feature
 
Agree with kenton. Laying out the part will make obvious mistakes like edge finder errors or dial miscounts obvious.

My Deckel has a tray that mounts to the table for holding gage blocks. Haven't had a need to use it but creating a stack and zeroing an indicator against it would be a good way to save the origin. Different stack lengths for different feature offsets eliminate counting issues and screw inaccuracies. I believe this is how old school jig-bores did things.

-Teryk
 
I am not concerned with holding .0001", or even .001"- I am concerned about being .200 off, because of having lost count of turns.

I did make a stop block for the table travel, but the lead screw easily overpowered it.
The plan now is to just make a simple scale with 5R (.01" ) divisions.
 
It can be as simple as a sharpie or grease pencil mark across the split between the movable and fixed portion of an axis. A rule can be used to give the number of turns anytime you forget. But unless I knew the mill, I'd work off layout lines before I'd count turns.
 
I pulled "Accurate Machine Work" off the shelf and did some remedial reading,as johnoder put it.
They talk a lot about the use of vernier scales and micrometer stops to retain and return to position. There is emphasis on lead screws not being consistently accurate.(in 1910 or thereabouts).
Good book. Makes me want a set of gage blocks.
 
I can see some remedial reading is in order - like holding tenths every day when DROs were way off in the future

Accurate Tool Work (1912) 1st Edition, 6th impression 217 pages with index, Goodrich & Stanley

No, that isn't a link

A few here - I would scroll down past the off shore jobs

Accurate Tool Work by Goodrich - AbeBooks
"Accurate Tool Work" book can be downloaded here: https://ia800209.us.archive.org/12/items/accuratetoolwor00stangoog/accuratetoolwor00stangoog.pdf
 
Two versions of Accurate Tool Work are available for free download at Google Books:
My Hauser jig boring machine has movable scales on X and Y with 0.05" graduations; very nice to keep track of the 0.1" part of your coordinate. You could set up the same thing with a pair of rare earth magnets used to stick a 6" ruler to the table or saddle, then you just need a pointer of some sort for zero. Maybe a paper clip and another rare earth magnet? gbent's method works as well, but doesn't tell you if you're at 0.8 or 0.6 like the ruler.

Cal
 
Sharpie marks running from table to saddle are quite effective and will get you within your .2 easily. Just make separate marks for each location you want to hit and label them so you don’t mix them up. When you are done with the job, wipe them off with a shot of brake cleaner and a rag.
 
Or travel indicators. I don't think I ever used the dial on a leadscrew on a mill ... okay, maybe for a real quick and dirty but.

If you can't count the number of turns, jeeze. Maybe wrap a piece of tape around a finger each time it goes around once, or something.

No wonder people think factory workers are stoopid.

Ya think? Have you ever lost count of anything? Never been interrupted?
You think those guys who wrote the book "Accurate Tool Work" needed tape on their fingers? They seemed quite enamored of a vernier scale on the equipment for precisely the same reason I am inquiring about it. I can assure you in 1920 they were far more aware of manual mill work than most are today.
The stupid worker, as you so kindly put it, is the one who refuses to accept the possibility something could go wrong, and hence takes no steps to try to proactively prevent error.
 
Two versions of Accurate Tool Work are available for free download at Google Books:
My Hauser jig boring machine has movable scales on X and Y with 0.05" graduations; very nice to keep track of the 0.1" part of your coordinate. You could set up the same thing with a pair of rare earth magnets used to stick a 6" ruler to the table or saddle, then you just need a pointer of some sort for zero. Maybe a paper clip and another rare earth magnet? gbent's method works as well, but doesn't tell you if you're at 0.8 or 0.6 like the ruler.

Cal

I am going to make a simple clamp to hold a scale on the table edge, as you describe.
BTW,did Hauser supply tape for the fingers with the machine? I am told it is the best way to keep track of position for stupid factory workers.
 
I've bought machines that had scales attached (glued and double face tape), with a rudimentary pointer. Schaublin includes an engraved scale on their lathe topslides with a pointer that can be moved by 10mm or so- it's super handy. I'm also a fan of the sharpie mark technique. Though I often work to microns I also do lose count of turns.
 








 
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