Spindle Thread Tolerances

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Aderhammer

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What's the tolerances of a 1"-8 spindle nose? I just got the parts from my uncle for my rose engine lathe and my chuck won't go on. The face plates require a good amount of force to get on. The top of the thread is about 5 thousandths larger than those on the spindle of my lathe. The drawing i made and handed to him i believe was labeled as an H grade.
 
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The tolerances are set by the manufacturer so the lathe mfg. is the only place you are likely to find the answer and I would guess it would be a difficult task to extract the information from them.

Did you see the thread by Dick?
http://www.penturners.org/forum/topic.asp?TOPIC_ID=36990
He changed out the bearings on his 1236 (also a 1 x 8 spindle) and now his Nova chuck will not fit on the spindle. The curious thing is the chuck will fit very nicely on his PSI lathe which is also a 1x8 thread and all of the other accessories (face plates and such) fit just fine on both lathes.

He has ordered a 1x8 die and is going to try to touch up the threads.

If you haven't already done so, you need to contract the maker of the lathe.

I am not sure I totally understand your original question. What are these parts you got from your uncle? Did he make the lathe?? Not quite sure what you mean by "top thread"; but a 1x8 thread should have a major diameter of 1". In the thread I referred to, we took some actual measurements and the major diameter on my JET mini was 0.990" and the thread on the 1236 was even smaller.

Your comment about "H grade" means nothing to me. Maybe it has some significance to others.
 
I'll look up the tolerances in the federal screw thread manual and try to post them at lunch time. Unless you have a set of thread measuring wires to measure the thread pitch the numbers will be pretty useless as you can cut a perfect thread pitch and then take up to 1/16" off the outside diameter and not notice a difference.
 
According to the Federal standard H28/2 there are 3 grades of 1.00-8 unc threads.

class 1A Major diameter (max .998-- min .9755)
class 1A pitch diameter (max .9168--min .9067)

class 2A Major diameter (max .998-- min .983)
class 3A pitch diameter (max .9168--min .9100)

class 3A Major diameter (max 1.000-- min .985)
class 3A pitch diameter (max .9168--min .9137)


I'm not sure what H grade you specified but that is usually how you would specify a tap that is to be used to allow for a coating or finish to be applied over the threads and they are as follows.

Pitch Diameter Limits for Taps Thru 1" Diameter.

H1 = Basic to basic plus .0005"
H2 = Basic plus .0005" to basic plus .001"
H3 = Basic plus .001" to basic plus .0015"
H4 = Basic plus .0015" to basic plus .002"
H5 = Basic plus .002" to basic plus .0025"
H6 = Basic plus .0025" to basic plus .003"


There is a lot more to threads than meet the eye and without the proper tools you are pretty much chasing your tail.

I hope this helps somebody.
 
Sorry must have been sleepy. The drawing was labeled 1-8 UNC - 2A. Randy, this part is from the plans for the mdf rose engine lathe, although i had drawn up my own parts as there were changes that i made to some of the parts. This part for example also has a morse taper.(yeah i know in the drawing there's no knock out bar or nothing, final piece has that fixed.)
mainspindleshaft-2.jpg
 
If yo have calipers, you can get a rough check by measuring down in the bottom of the 'v' of the thread. (Don't worry that you can't get all the way to the bottom) Check the spindle on the lathe, and the part that was made for you and see what the difference is. I have made a few parts not having a gage by doing this.
 
Thanks paul will do that, he matched it to a nut that he had on hand labeled H2. The difference could be 2 or 3 thousandths of an inch off! I think i'll stick w/ wood working:D This metal stuff is too complicated[:p]
 
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