# 16TPI vs 20TPI



## Brass_Machine (Feb 4, 2011)

Have to replace some pieces on my mill. Basically my Y axis bit the dust... In the process of finding the parts for my mill, I see there is a choice between 16TPI and 20TPI on the lead screws. Since I am going to replace both X & Y (getting the longer lead screw for X), which is a better option? I have 16TPI now...

Thoughts? I am going to order this afternoon, so whatever advice I can get.

Eric


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## doc1955 (Feb 4, 2011)

??? If you change you will need to change you dials as well. ???


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## Mike N (Feb 4, 2011)

You will need to get the same TPI as the original screws had or your dials will be completely off.


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## Jasonb (Feb 4, 2011)

I'd go for 20tpi then one turn of the wheel is 0.050" easier to keep track of than 0.0625" which the 16tpi will give. But as said the handwheels will need re engraving

Jason


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## kvom (Feb 4, 2011)

If you have a DRO it won't matter, but 16TPI is less cranking.


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## TroyO (Feb 4, 2011)

Littlemachineshop has a full kit for doing just that... may even save you a few $ over getting all the parts?

http://www.littlemachineshop.com/products/product_view.php?ProductID=1764&category=879658189


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## wareagle (Feb 4, 2011)

The 20TPI would be a bit more precise but would require a new dial as the others have said. If the 16TPI has been working for you, then why reinvent the wheel? 

My $.02 worth: I'd go 20TPI if they have the correct dials and they weren't stupidly expensive, otherwise I'd go 16TPI and never look back. 

_Yes a new dials could be made easy enough, but I am lazy that way. Especially if they are available._


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## Brass_Machine (Feb 4, 2011)

Obviously the hand wheels would need to be changed out as well...

I wanted to know if there was any performance reasons to get the 20TPI over the 16TPI.

I think I will go with the 20TPI since I am replacing everything anyway.

Thanks

Eric


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## Brian Rupnow (Feb 4, 2011)

The 20TPI will be easier to crank, but will move more slowly and take more revolutions of the wheel to get from point A to point B. The 16 TPI will be harder to crank, but will take less revoutions to get from A to B.


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## TroyO (Feb 4, 2011)

Hmm, I don't think the wheels have to go... the dials slip on to them. Even if you don't get that LMS kit, it will show you all the parts that are required.

I debated the 20 TPI changeover myself.. the "1/2" of the "62-1/2" dials drives me nuts. In the end, I think I am going to put the $60 in to a DRO. 

But, if I had to replace anyway, like you do... I'd get the 20 TPI screws and dials in a heartbeat! 

(grumble)
I mean really.... do they sell fractional centerfinders? Have you seen a machining plan marked out in 16ths?For woodworking... 16ths/32nds and occasional 64ths sure.. for machining I want nice round decimal values. 
(/grumble)


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## Brian Rupnow (Feb 4, 2011)

Troy---The spacing of the graduations on the dials relates mathematically to the pitch of the screw. If you change to a different thread pitch, the dials will give incorrect readings. For someone like me who uses those dials all the time to position work for milling, that would be a disaster!!!


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## TroyO (Feb 4, 2011)

Ohh, I get why there are 62.5 graduations..... what I don't get is why they chose a 16 TPI/16th of an inch per turn leadscrew in the first place. It just doesn't make sense to me to choose a /16 division on a machine designed for /10 math, LOL.

Ohh, and about the dials... yes, they would need to be replaced. The handwheels themselves are universal, though. The new dials just slip in place on to the old handwheels.


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## tel (Feb 4, 2011)

You'll probably find it's a hang over from the 8tpi lathe leadscrews. 8tpi on a lathe is _good_, 8tpi on a mill would be _not as good_. Screws on my RF30 are 10tpi.

That kit looks to be good value tho' - wonder if it would fit my metric HM10 (X2)


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## TroyO (Feb 4, 2011)

If you hit the "compatability" tab, it lists the "Hare & Forbes HM-10 Mini Mill Drill" as being compatable.


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## tel (Feb 6, 2011)

Thanks Troy, I missed that.


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## Tin Falcon (Feb 8, 2011)

20 TPI is a common screw pitch for machines 1/20 = .050 
a bit easier and more logical than 1/16 = .062 
if you plan to use the dials much easier to keep task of counts. 

Save yourself some aggravation put in ball screws and convert to CNC. :
well maybe not less aggravation DAMHIKT :big:
Tin


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