Author Topic: Offtopic technical question  (Read 1197 times)

mark_m

  • ROV Full Member
  • ***
  • Posts: 35
  • Imagination is more important than knowledge.
Offtopic technical question
« on: June 17, 2005, 09:14:23 PM »
I just bought a digital vernier gauge that is supposed to be accurate to .01mm. I figured it's a good investment because with that acuracy it doubles as a micrometer. When I got it home I decided to test it on the 8x20 machine screw I bought that goes into my visions banjo fitting when I bleed the brake.

To my surprise it measures 20mm lengthwise, but exactly 7.90 mm when I measure the width by putting the vernier around the thread. 7.9mm seems like too round a number to be an inacuracy in the vernier gauge.

Does anyone know why a metric screw that is supposed by be 8x20 is actually 7.90mmx20mm?

Thanks.

Mark.
ps: The screw was bought at OSH in their metric screws section.

Blake

  • ROV Senior Member
  • ****
  • Posts: 1025
    • Photos of my builds
Re: Offtopic technical question
« Reply #1 on: June 17, 2005, 09:24:44 PM »
haha

when i got my set from harbor freight (6" digital calipers) i measured the same thing.

7.9mm.  (best i can think of, which cooresponds with my friend the machinist) is when they turn the bolt for the threads they take a little off, and plus you dont want it tooo tight, or else the bolt wont slide in.  basically a little "slack".


or thats what i was told.  to me seemed to make sense.



Blake
"At first it's like a new pair of underware... Frustrating and constrictive.  But then, it kind of grows on you..."

Junior

  • ROV Full Member
  • ***
  • Posts: 59
  • Riders of Vision
Re: Offtopic technical question
« Reply #2 on: June 17, 2005, 10:03:08 PM »
That is correct. It was a 8X20 until the thread pitch was tooled on the Outer Diameter bring the thread to correct size. The same on Inner Diameter threads. If you tap a 1/2" hole with a 1/2" tap, it should check a little larger. OD threads are normanly cut with a slight minus tolerance and  inner diameter threads with a plus tolerance. The plus and minus tolerance is normaly determined for the application it is design for. ( I Think ::)

mark_m

  • ROV Full Member
  • ***
  • Posts: 35
  • Imagination is more important than knowledge.
Re: Offtopic technical question
« Reply #3 on: June 17, 2005, 11:46:51 PM »
Awesome, thanks guys! Thanks Junior - that makes perfect sense.

 

Related Topics

  Subject / Started by Replies Last post
Technical Questions.

Started by Joshua Johnson Board Archives

5 Replies
1141 Views
Last post June 22, 2004, 11:12:36 PM
by h2olawyer
4 Replies
1462 Views
Last post June 09, 2005, 11:07:02 PM
by Lucky
25 Replies
3257 Views
Last post January 17, 2007, 10:45:24 PM
by munkyfistfight
12 Replies
2002 Views
Last post February 02, 2009, 09:28:09 PM
by Rick G
10 Replies
302 Views
Last post July 30, 2021, 08:59:15 AM
by Prophet Of Doom