Position Tolerance for Dowel Pins.

[Vishal2015]

Hello Everyone,
I need some help to decide the position tolerance value for distance between 2 dowel pin holes.
Details:
Need to find out position tolerance value for 2 holes on mounting bracket of Dia 10H7 and 100 mm apart.
1. Fit required: Dia 10 H7/h6 Transition fit.
2. Two Dowel pins (OD Dia 10h6) are mounted on base 100+-0.005 mm apart.
Questions:
1. How to calculate position tolerance. Will it be same as calculating fixed fastener position tolerance i.e. MMC hole – MMC shaft = 2 x Tolerance.
2. As MMC of hole and MMC of shaft is dia 10, should I use Zero Position tolerance with MMC modifier?

Thank You,
Vishal

 

[drawoh]

Vishal2015,

In GD&T, dowel pins are equivalent to screws. Unlike screws, you use very small clearances, typically too small for positional tolerances to guarantee things will fit. You can...

[ol]
[li]Slot one hole[/li]
[li]Use a diamond shaped pin in one position.[/li]
[/ol]

Your as-fabricated tolerances make your assembly repeatable, not accurate.

Alternately, you can assemble your two pieces in the exact position you want them, and then drill and ream both pieces for the dowels. Your dowels machining and installation are part of your assembly process, not your fabrication process.

I love to use 0[ ]positional tolerances at MMC. Always, I make the maximum acceptable holes grossly oversize to provide manufacturing allowance. With dowels, this is not an acceptable solution.



--
JHG

 

[KENAT]

Simplistically yes it's similar to calculating fixed fastener case.

Are you planning on replacing 100+-.005 mm with 100 basic & appropriate position tolerance?

I fear your tolerances might end up unrealistically tight, but don't remember the H7/h6 numbers off the top of my head and won't go looking for them.

Suggestion - does it need to be 2 holes or can it be one tight hole, with the other hole replaced by a slot of tight width but with extra length to accomodated tolerance variation?

Alternatively can some king of spring pin/roll pin that has a little flex be used?

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[juergenwt]

One pin has to be a diamond pin.

 

[Vishal2015]

Thank You so much Drawoh, Kenat and juergenwt for your response.

I was planning to replace 100 to basic dimesnion, but now i will not do that.

Diamond pin or Slotted spring pin will be a good option.

Also slotted hole is good option but i dont know how to use it on drawing for dowel. should I use Dia10H7 tolerance i.e. +0.015/0 to slot width i.e. 10+0.015/0 mm.

Thank You.

Vishal

 

[KENAT]

Quit being so obsessed with standard limits and fits and if necessary consider doing some thinking/research of what the functional requirements and manufacturing limitations really are.

You probably should be using a basic dimension with appropriate position tolerance on the features.

Just to be clear, the slot isn't for the the part that the dowel pin is permanently installed in, it is for the mating part.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​