Crossfeed and carriage dial accuracy on mini lathes

D

D.sebens

H-M Supporter - Silver Member
H-M Supporter - Silver Member
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Mar 27, 2022
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Hi there. I have a 7x12 mini lathe. The dials “say” they are in thousandths but seem to cut more than they say. They also have a metric number on the dial. Is the metric number the accurate number? I know it’s a cheap lathe and what not, just trying to figure out what I should do to trust the increments on the dials. I haven’t machined in about 15 years but I remember enough to get me in trouble.
My first project on this is a replacement gland for the loader on my tractor. The original was cast iron and was cracked. I’m making the new one out of 2024 aluminum. It’s going pretty well so far.
 
It's quite possible it's metric. Verify with a measuring instrument of your choice, then you will know
1 MM = 0.03937 inch
-M
 
As Mark said, I'd suggest just setting up a dial indicator and measuring how far it travels over a little bit of a distance.
 
Thank you. It says 0.001” per increment but also 0.025mm per increment. I’ll put a dial indicator on it to see. Hopefully they mm is accurate. It’s easier to convert to metric than solve for X every time.
 
D.sebens said:
Thank you. It says 0.001” per increment but also 0.025mm per increment. I’ll put a dial indicator on it to see. Hopefully they mm is accurate. It’s easier to convert to metric than solve for X every time.
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.001" is the same as .025mm, so if it doesn't match for inches it won't for metric.

One thing to check: are you expecting it to be a radius measurement and it is actually diameter?
 
No. More like a .010 cut ending up 0.022-0.025”or so. I understand radius vs diameter with the increments. It was with carbide tools in the aluminum. I have some hss blanks to grind up now. I set the tool at the center line. Maybe it was just hogging in a little. Or maybe I take it for what it is. I’ll check with the indicator, and try hss. Also I’ll take some light passes and see about them.
 
You might be experiencing some deflection of the tool, or carriage itself. Make sure the gib adjustments are as snug as you can make them while still allowing movement. Carbide tools, especially cheap "blunt" ones often require too much force. HSS tools work best on small lathes.
-M
 
I’ve adjusted the gibs. The carriage adjustment is a terrible design and I’ve concluded that you just do the best you can. This was with 1/4 tool stock and China carbide. It was shimmed up to center line. We will see how it goes with 5/16 hss.

I agree carbide isn’t suited for this lathe. I bought some cheap 1/2 shank boring bars that are carbide. I don’t have any stock on hand to make my own at this point and I didn’t know carbide wasnt the best choice. Boring with .005 or less on a 1-1.5” diameter yields smooth feeling results. You can still see chatter in it but cannot feel it. Any more and there’s noticeable roughness. Luckily the rest of the boring is not full depth and I can do it with a standard 5/16 tool blank. I figure that should help.

I still need to replace the roller ball bearings in the head stock with tapered ones. I have them, just was too excited to make my part. I figure a hydraulic gland needs to be smooth, but not beautiful. I figure it will be field fix finish.

I also made the mistake of unchucking it to test fit it. That Chinese 3 jaw was a pain to recenter the stock in. I think the tolerances in the chuck were allowing it to not fully center since I had indexed the part to the chuck before removal.
Side question, the finish od is 2.25” with an id of 1.5”. Ive chose to make it longer then part to length. Will the lathe tolerate parting .75” deep on this diameter okay or should I use my band saw, rechuck, and face?

I’ve never parted before.
 
1.25mm is .0492" vs. the .050" pitch equivalent of 20 tpi. Plenty of mini-lathes say "close enough", the LMS and Micro-Mark lathes might actually use true english pitch screws. But this isn't going to be the cause of as much inaccuracy issue you're describing.

Mikey from this site has a great thread going into boring on a mini-lathe - go check it out.

Parting a 2.25" OD x 1.5" OD chunk of aluminum on the mini-lathe is going to be challenging the first couple times. If you can't afford to scrap your current part, consider the bandsaw then face to length. If you don't mind needing to make another gland, then by all means give it a shot!
 
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