# Truing up micro-lathe jaws?



## Cap'nBill (Dec 27, 2008)

I have a 'standard' Chinese made 7 x 10 lathe which is generally well worth the $200 I paid for it. Recently, I started working with some really small diameter rod and found the 3 jaw chuck is maybe .005 off-too much for steam cylingers, rods etc.!. With my 4 jaw, I can usual get to within .002. Anyone have any suggestions how to get the 3 jaw any closer? I've tried a small grinding 'wheel' held in my MT drill chuck in the tailstock, but I can't really tighten the jaws enough......if that makes sense. Seems if I hold the material at the outside of the jaws, it's more accurate but long pieces of 1/4" rod, or smaller when held by the full depth of the jaws. It would appear the inner surfaces are not parallel. Any thoughts? Bill


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## Michael Glavin (Jan 2, 2009)

Bill, 

This can be done, the procedure is to utilize a high speed rotary tool mounted on the cross slide accurately and a diamond bit. That said as you likely know three jaw self-centering chucks are known more for convenience than accuracy. In your case you describe a short-coming that may well be addreesed by truing your chuck IMO. 

Michael


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## Jack - Freshwater Models (Feb 17, 2008)

Bill, 

Be sure that it is the jaws before you do any "truing" 

Remove the chuck from the lathe and indicate the bearing surface of the spindle where the chuck fits on the spindle. Then clean the chuck bearing surfaces where it attaches to the spindle. Re attach the chuck to the spindle making sure that there isn't any play. Indicate the chuck body to make sure it is concentric to the spindle. If not concentric to the spindle you see where the problem is. If concentric then check to make sure the jaws and scroll are clean. Indicate again and see if the jaws need truing. 

I have a couple of chinese lathes and was amazed at the quality of the chucks but maybe you got a bad one. My 7X12 grizzley lathe is very true. 

Go at it methodically before your start to remove any metal. 

Good luck, 

Jack


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## xo18thfa (Jan 2, 2008)

Bill: I am going to second Jack on this one. You would be surprised how hard a chip can stick to another surface and throw things off. And actually 0.005" on a 3 jaw is not outside the ball park. They can get worse. Another option to cutting metal is put a shim under the offending jaw.


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## hawkeye2 (Jan 6, 2008)

Bill,

Here is a link to Varment Al's Mini Lathe page on which he describs truing a 3 jaw chuck. There is a lot of good info on his site.

http://www.varmintal.com/alath.htm#Truing


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## Cap'nBill (Dec 27, 2008)

Thanks for the advice and info, guys. I've really been happy with this little lathe. Bill


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## Les (Feb 11, 2008)

Posted By Cap'nBill on 18 May 2010 08:28 AM 
Thanks for the advice and info, guys. I've really been happy with this little lathe. Bill 



Cap,

Jack's on the money. Read 'n Heed. 

Now I want to advance a thought for your future consideration: You said "Small (or tiny--I forget and it's late, again) diameters". A number in SAE would help. Also, another disclaimer: a chuck that's out needs fixing. First.

Now for what crossed my mind: Working VERY small diameter items can benefit from a small, precision chuck meant to take 'tiny' work or bits. Just a thought. I believe MicroMark boasts itself of offering small, precision chucks. You'd have to check 'em out. The Little Tool Seller or whoever is another place to look. That's not the right name, but Google Minilathes and you'll turn 'em up. Several, in fact, that offer cool aftermarket items.

Glad you like your lathe.

Les


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## Michael Glavin (Jan 2, 2009)

All good advice, but Bill mentioned and or suggested the problem was realized when the full length of the jaws were utilized verses holding and indicating things at the ends\tips. Wouldn't this suggest the problem was more likely than not the jaws in of themselves? 

Michael


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## Jack - Freshwater Models (Feb 17, 2008)

There are a number of factors at play. IF the chuck holds a length of known round and straight material like drill rod AND it indicates without run out the chuck and jaws are running true the outside jaws are running true. Indicating the inside jaws is more of a problem since one really needs a bit or precision tube to indicate correctly. One does have to indicate both near the chuck jaws and further away from them to determine both axial and radial runout. It's a lot easier to show than describe in words. More years ago than I care to admit .002-.003" RO on a 3 jaw chuck was considered acceptable. My 7X12 has about .0015 runout or less. A simple bit of swarf can throw a chuck out by .005 (or more on a long piece) both axially and radially quite easily. 

W/O putting my hands on the lathe and chuck w/indicator it's hard to preciely diagnose the problem. I still say it is best to clean up everything concerned and methodically determine precisely where the error is. 

When possible it is best to hold material bearing on the full length of the jaws surface. One possible problem is that the jaws are tighter toward the headstock than towards the tailstock. Not an easy problem to correct. My 7X12 3 Jaw chuck will hold 3/32 stock but not anything smaller. For test purposes I suggest using .5 or .75 dia rod. If you want to get carried away with it get a precision test rod for about $50. 

The 7X lathes are a tremendous bang for the buck but they aren't really as precision as what you might find in a commercial shop. I spend an afternoon tuning my lathe by scraping the saddle to get a better bearing surface on the ways and cleaning a lot of red grease from every nook and crany. The worst part of my 7X12 is the tailstock which is a piece of junk as they are on all 7X lathes. 

It might be worth it to purchase a chuck. You could spend many hours trying to solve a problem that could be easily solved by a new chuck. If the new chuck runs out unacceptably the spindle is suspect. 

Mi dos centavos. 

Jack


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## Allegheny (Jan 2, 2008)

For turning small diameter, high precision work first make sure the spindle is accurate. After determining that, don't bother with a chuck - use a collet set up. I don't know what size collets fit the 7x10 minis, but I'm sure you could hold at least 3/8" diameter stock.


If you must use a chuck, go with an independent 4-jaw. They are not as convenient as a 3-jaw "scroll" (i.e., self-centering) chuck, but they are very accurate and once you get used to setting them up, take little extra time. A big advantage to them is that you can chuck up irregularly shaped things and bore holes off-center by indicating the center of the hole to be drilled and not the circumference of the workpiece. A good example would be the axle bore of a driver and the offset hole for the drive rod boss pin.


Brian


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## Chucks_Trains (Jan 2, 2008)

I had trouble with my lathe having over .003" runout so I did exactly as suggested. I removed the chuck & dialed the spindle..was amazed to find that it had only .0005" of runout!! I cleaned up the back of the chuck, remounted and used a dial indicator...the biggest culprit was the bolt holes in the spindle have to much slop so I snugged them up and used a deadblow hammer to center the chuck while dialing it. Now my mini-lathe has .001" runout and that I can live with!! New precision chuck's can cost lots of $$$..more than the lathe cost!


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## SE18 (Feb 21, 2008)

I wish that when you purchase a lathe you could choose a 3 or a 4 chuck rather than every manufacturer choosing a 3 for you.


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## Jack - Freshwater Models (Feb 17, 2008)

The chuck of the 7X mini-lathe has a recess and the spindle has a boss and they are supposed to fit together tightly. The studs and nuts shouldn't have anything to do with run out. That being said you may have a lemon that has a loose fit allowing you to "adjust" the fit with a hammer. There is no easy fix. You might be able to swap out the spindle if that is undersize or remake the back plate of the chuck. 

Jack


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## Ger  (Jan 13, 2009)

There is no need to true the chuck. It is unlikely you can make the chuck run true. If it was that easy, you would not have the problem. 

The standard procedure is to make a split chuck, ( unless you want to spend a lot of money on a collet chuck). 

For example, to turn a piston on a 5/32 rod proceed as follows, 

Chuck a piece of 3/8 rod, brass is good, in the 3 jaw chuck. Face the end, center drill, drill through with No. 24 drill. Ream 5/32. This should bore a hole dead true wilh the center line of the lathe mandrel. 

Make a center-pop opposite No 1 jaw. Remove the bush, split it lengthwise with a hacksaw through to center hole. Rechuck, align to No 1 jaw, ream to remove any burring. When the piston rod is put in the hole the rod and piston will run true.


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## xo18thfa (Jan 2, 2008)

Posted By Jack - Freshwater Models on 24 Jun 2010 12:31 PM 
The chuck of the 7X mini-lathe has a recess and the spindle has a boss and they are supposed to fit together tightly. The studs and nuts shouldn't have anything to do with run out. That being said you may have a lemon that has a loose fit allowing you to "adjust" the fit with a hammer. There is no easy fix. You might be able to swap out the spindle if that is undersize or remake the back plate of the chuck. 

Jack 

When I put the 3 jaw on my Atlas 6", I put a blank back plate on the spindle and turned it to the recess on the chuck. The 3 jaw is almost dead on. It gets even closer when I tighten each key just a little at a time.

Recently bought a ready made back plate and 4 jaw chuck for the 9 x 20 import. It's off by over .050" (yes, almost 1/16"). I am going to cut that boss off and re turn it.

Do the 7x lathes come with a removable back plate?


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## Jack - Freshwater Models (Feb 17, 2008)

Bob, 

My chucks have intragal chuck/backplate as far as I can see. Stuff made for the 9X20 seem to be quite variable in quality. I have always mounted the backplate and machined it before fitting to a chuck. Boy I wish I could afford a Hardinge and a place to put it!!! 

J


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## xo18thfa (Jan 2, 2008)

Hi Jack: The 4 jaw that came with the Atlas 6" runs perfectly true on the periphery of the chuck body. The 3 jaw and 4 jaw that came with the 9 x 20 are OK. The new chuck/backplate for the 9 x 20 came from a different company then where I bought the lathe. I bet the backplate turned perfectly on thier machine.

I agree. I would like to get a Myford ML7. It's the ultimate hobbyist lathe. But, until we win the "Super Lotto" the import stuff will have to do.

Bob


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## RimfireJim (Mar 25, 2009)

Posted By xo18thfa on 25 Jun 2010 04:37 PM 
Hi Jack: The 4 jaw that came with the Atlas 6" runs perfectly true on the periphery of the chuck body. The 3 jaw and 4 jaw that came with the 9 x 20 are OK. The new chuck/backplate for the 9 x 20 came from a different company then where I bought the lathe. I bet the backplate turned perfectly on thier machine.

I agree. I would like to get a Myford ML7. It's the ultimate hobbyist lathe. But, until we win the "Super Lotto" the import stuff will have to do.

Bob

Bob: Nothing is "perfectly true". It's just better than you can measure and/or care about.

I haven't seen a Myford, but according to this page http://www.lathes.co.uk/myford-ml7/ it is similar to my 6" Atlas. Those are no comparison to a Hardinge HLV tool room lathe or equivalent, which run so true and smooth you hardly know they're turned on (and will set you back about 10X that of what an Atlas/Craftsman will cost). I've been lucky enough to have access to a tool room lathe during most of my engineering career, so my Atlas sits at home unused. It would be gathering dust except for the fact that it is covered by the original cardboard box, on which I've piled all manner of odds and ends! One of these days, though, when I won't be working and thus will have time to putter in my home shop, I hope to need it for some projects.


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## Jack - Freshwater Models (Feb 17, 2008)

Jim, 

I have to agree with you about the Myford which is OK but way over rated. IMHO if a lathe doesn't have either prismatic or dovetail ways it isn't going to work bvery well over time. 

J


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