RF-30 clone issue

PhillT

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I was thinking about a DRO for my mill, but have been holding back because I like the simplicity of the dials, and now that I have converted the fixed dials to being re-settable (zero-able) the appeal of DROs has faded even more.

The only thing that would have sent me down the DRO path would have been a vast improvement in accuracy, as measure against the dials, so I set about testing that very thing.
The first step was to determine the accuracy of my dial indicator against my Mitutoyo vernier, and the D.I. came up being as accurate as the vernier, so the testing began.

The results were as follows:
"X" axis over 9mm of travel came up minus 0.05mm
"Y" axis over 9mm came up as spot on
"Z" axis over 9mm came up minus 0.5mm

I would like to measure the "X" axis over a longer distance to see if it gets worse, and I will do that with a calliper soon.
The "Z" axis was a real surprise. I never expected it to be so bad, but thinking about it, unlike the threads on the feed screws of the X & Y axis, the Z is a rack & pinion, which may well explain the poor accuracy, although you would think that the dial could have been marked to suit. That of course would make for a quite confusing scale.

The answer to the "Z" axis problem was to go the "Poor mans DRO" route and use a vernier as a DRO, which has proved to be an excellent fix. I used a carbon fibre ebay cheapie which runs to only one decimal place, but the dial is accurate enough to adjust to the second decimal place if needed.

If the "X" axis error proves to be greater over longer travel distance, then the 2-axis DRO route might have to be revisited.
 
Did you see the same error using the fine feed on the Z?


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The fine feed is the one with the dial, so that is the one I tested David.
 
The fine feed is the one with the dial, so that is the one I tested David.

Oh right. Sorry, mine is the same.


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There was a recent thread regarding accuracy of the z axis dial. I have an RF30 clone, c.a. 1980. My z axis dial reads .085"/revolution. For ten complete revolutions, the DRO read .849" The fine feed on my machine has a worm gear driving a pinion which is coupled to another pinion gear which drives the rack. Other machines may use a different combination of gears and may approximate the distance traveled to make the dial divisions a nice even number. My machine uses inch lead screws for x and y travel but I have used other machines the have metric lead screws and round 3.937 to 4.000 The Grizzly G0755 does this as well as the G4000 and G0602 lathes.
 
My z axis dial reads .085"/revolution. For ten complete revolutions, the DRO read .849" The fine feed on my machine has a worm gear driving a pinion which is coupled to another pinion gear which drives the rack.

That is the same mechanical setup as mine, and I suspect all the RF30 clones.
You are fortunate to have a dial that is so accurate.
I have a feeling that the mechanics of the fine feed drive are in fact identical in the Imperial and the Metric machines, based on the math.

0.085"/revolution equates to 2.159mm/revolution, and mine is giving 2.15mm/revolution.
 
Here is what I wrote in a thread on Nov. 10.

My RF30 clone has a rack on the quill with a pitch of 8mm and driven by a 10 tooth pinion resulting in 80 mm of quill travel for one complete revolution of the pinion. The fine feed worm drives a 37 tooth gear and has a nominal quill travel of .085"/revolution. In actuality, 37 revolutions of the fine feed advance the quill 80mm or 3.1496". Therefore, one revolution of the fine feed advances the quill 3.1496"/37 or .08512". This is verified by comparison with the DRO.

Gear ratios have to be a combination of whole numbers. Add to that the conversion from metric to inch measure.and it is extremely unlikely that you would have a dial that read inches exactly. If it were a metric mill and the worm gear had 40 teeth, one revolution of the fine feed would be 2.00mm. I suspect that when they converted the mill for Imperial use, they wanted to change as few components as possible, in this case a different worm and worm gear which would still fit in the gear housing.
 
I have an Excel EC30B which is a RF 30 clone. The X&Y are spot on whereas the Z is off by the same amount as RJ's. I plan to add a dial caliper to measure the Z.
 
I first added a digital caliper to the z axis but within six months went to a three axis DRO. I would do it again in a heartbeat. The DRO adds accuracy better than could be achieved when the mill was new.
 
RJ, that has me wondering why my Z is 2.15mm/rev of the fine handle. Perhaps it was inadvertently fitted with a worm gear of something other than 40 teeth either at the factory or at a later date.
If i ever have cause to dismantle it again, I'll be sure to check.
 
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