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Making a thread dial 4 tpi lead screw emco v13

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mds30br

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#1
From what I have read with a 4 tpi lead screw I need a 16 tooth gear for my dial? Any specific pressure angle?
I have an Emco v13 and have not been able to locate a thread dial for one. I have a friend who is able to laser engrave a dial for me ( I have a mill but lasers are way cooler) and I figure I can machine some aluminum for a housing unless there is a better metal for the job.
And if anyone happens to have the specs on bearing tolerances for this machine that would be great. The gentleman who sold it took the spindle apart and when he put it back together there is about .004" radial and about .010 axial play. I got a little nauseous when I lifted the chuck while mounted and the spindle nose moved.
Mike
 

4GSR

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#2
Use a 12 DP 14-1/2 degree pressure angle 16 tooth gear.

I made one many years ago using a phenolic gear that Boston gear sold. Worked out perfectly, even though the gear teeth were not cut to an angle to match the lead angle of the thread on the lead screw. Doesn't have to be perfect.
 

mds30br

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#3
Thanks insurgent K, I had a feeling that the pressure angle was more important if it was being used for an actual drive gear and not a passive role as a thread chaser.
Mike
 
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4ssss

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#4
You don't need a thread dial to thread on a lathe. Just keep the carriage half nut locked like your threading traditionally, and when you get to the end of your cut, reverse the lathe motor without disengaging, and forward again to do another cut. (you can stop the lathe in between to dial out your cross slide, and then back in again) As long as you don't disengage the half nut, you'll always pick up the thread at the right spot.
 

mikey

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#5
Emco made a thread dial indicator for the V-13 but I cannot find an image anywhere. For the 4 tpi lead screw, you would need a 16 tooth gear as Ken indicated. Emco's TDI's were unusual in that they had three gears on a common shaft that allowed you to cut Imperial and Metric threads, providing you had the right change gears. I don't know what the V-13 TDI looked like but here is the one used on the Super 11:


129359d1422997985-opportunity-buy-emco-compact-10-a-s11-threadingdial.jpg

The housing is simply a cast aluminum affair and the slot allowed you to engage the proper gear for the thread you needed. If I recall, the 16t was for Imperial and the 14t allowed you to cut most Metric threads. I can't recall what the 15t gear was for; maybe diametral or modular pitch.

In case you don't have the Instruction and Parts Manuals, I am attaching them here. I looked and cannot find the TDI anywhere in the manual, although they list it as an accessory so Emco made one. Nothing on ebay right now but one will show up eventually. If you opt to wait for one and buy it, jump as soon as you see it because these parts are no longer available and competition is fierce.
 

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mikey

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#6
And if anyone happens to have the specs on bearing tolerances for this machine that would be great. The gentleman who sold it took the spindle apart and when he put it back together there is about .004" radial and about .010 axial play. I got a little nauseous when I lifted the chuck while mounted and the spindle nose moved.
Look at parts 85 & 87 on page 8 of the IPB. The tapered roller bearing is a P5, the equivalent of an ABEC 5 bearing. A P5 bearing has about 0.0002" of radial run out and 0.0003" of axial run out. It is the lowest of the precision bearing class but still decent. The preload on this bearing set is adjustable; see page 23 of the manual to access the adjuster.

Emco says, "... turn the screwed ring until the spindle can be lightly revolved by hand." That is pretty vague and not very useful. The way the factory did this was used on every gear head lathe they made. This quote came from an Emco factory engineer who actually did this procedure:

"With the machine in neutral, disengaged from lead or hex screw (if applicable), and either the 3 or 4 jaw chuck installed, spin the chuck by gripping one of the opened jaws on top of the chuck and spin strongly. One revolution of the chuck is perfect. Less is too tight or bad bearings and more than 1.5 revolution is too loose."

So, how strong is "strongly"? As hard as you can spin it by hand. Use gloves to prevent the chuck jaw from taking off meat when you do this. Be sure to mark one jaw so you can clock the rotation. Note also that this adjustment is done COLD, not with the lathe warmed up. The assembler made this adjustment before the lathe was fully assembled so this procedure is not done on a warmed up lathe.

The V13 was made to one of two DIN specs - the standard 8606 or the 8605 "tool room standard" and I don't know which one yours was made to. My Super 11 CD was made to the tool room standard and may differ from yours but mine has zero radial and axial play and I suspect you can adjust yours to very near that if your bearings are, in fact, class P5 or better. The only way to know is to remove the spindle and check it but before you do that, I would suggest you try adjusting it first. If you can get the spindle run out to a decent level, do the warm up test Emco suggests in the manual. Run it at high speed for 15 minutes and check the "warmth" of the bearings.

Emco typically used FAG bearings in their lathes and that is the brand I would use if this were me. I initially wrote about the proper way to grease these bearings but they are lubed by the oil inside the headstock - if you get the former post in an email, ignore that because I'm an idiot and was thinking about the Compac 8 that I worked on not too long ago.

You asked for the "specs of the bearings"; hope this helps.
 
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mds30br

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#7
That is fantastic information, Mike.
I can spin the chuck easily at this point and it will rotate several times before coming to rest. I have a spanner wrench coming so will be able to tighten the collar properly. The bearings are, in fact, FAG as I checked them last night.
Hopefully I will be able to get this thing into spec!
Thanks again,
Mike
 

mikey

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#8
Hope it goes well. Once you get them adjusted to your liking, be sure to do the "warmth" test they lay out in the manual to make sure your adjustment don't stress the bearings. Then check for concentricity in the spindle with a dial test indicator to document what it is. Also check the D1-4 register to make sure you get the same thing. Once that is done you should be good to go.
 

benmychree

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#9
Use a 12 DP 14-1/2 degree pressure angle 16 tooth gear.

I made one many years ago using a phenolic gear that Boston gear sold. Worked out perfectly, even though the gear teeth were not cut to an angle to match the lead angle of the thread on the lead screw. Doesn't have to be perfect.
Technically, the gear would be done in circular pitch, not diametral pitch, as it is not meshing with a diametral pitch screw; that said, the 12DP gear with 14-1/2 deg PA will be a close match for a 4TPI screw. The usual four numbers on the dial each represent 1" of travel along the screw. So far as threading without a dial, it can be done if the lathe can be stopped accurately at the end of the thread, the half nuts opened, and the carriage returned to a location in EVEN INCHES to the starting point. Also, with TPI that are a factor of the lead screw pitch, four in this case, such as 2,4,8,16, 32,etc., the half nuts can be disengaged, the carriage returned to the starting point and re engaged at any point and the thread will track.
For newbies, the threading dial must be engaged on numbers or lines for even threads (with an even threaded lead screw), on numbers only for odd threads, on opposite numbers for 1/2 threads and on one number (only) for 1/4 threads, plus the info given above for threads that are a factor of the lead screw.
Metric threads cut on a lathe with an English lead screw (only possible with transposing gears) must be completed without disengaging the half nuts.
 

markba633csi

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#10
Something about that thread dial looks puzzling- if the entire unit moves up and down when you loosen the socket screw, then aren't the gears
in the wrong order? Take a look- it looks like the end gear should be a 16 and the one furthest from the bottom should be 14. What am I missing?
 
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