Positioning pins 1

[davidrdguez]

Hi there!

I'm in charge of the design of an assembly.

We have to position some little parts very accurately; in these parts there are 3 holes: two M6 screws and one D12 hole for a pin for positioning. The hole is D12H7 and it has a depth of 7 mm.

I have to check the pin and the hole on the table where the parts are placed.

It is the first time I do something like this. I've been checking in internet but I can't find exactly what I'm looking for.

Can I get directly this pins from a manufacturer? How should they be? D12h7? Should I make it tighter?

The hole in the table also D12H7?

I attach a sketch for this problem.

Thank you very much!

Regards,
David

 

[KENAT]

http://www.roymech.co.uk/Useful_Tables/ISO_Tolerances/ISO_LIMITS.htm

Depends a lot on function - how well aligned do they need to be, what type of fit do you want with reference to the above linked chart?

Also, if orientation is significant one usually uses either 2 pins with 1 hole & one slot, or 1 round pin & 1 diamond pin with 2 holes, or even just holes but with some kind of spring pin to allow for the slight misalignment.

Posting guidelines faq731-376

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

 

[pmarc]

There is no sketch attached - at least I can not see it.

If I understood you correctly, you want to build something like hard gage (counterpart) for checking if all holes are in their correct position and within limits of size, am I right?

 

[davidrdguez]

Right! i forgot a click for including the picture.

The piece to align is a kind of cylinder, so we only need a pin.

According to the table it seems i would need a H7 h6 or even k6.

Pmarc, what I need is just position some parts very accurately, I trust people in the workshop will make the holes properly

Thank you all!

 

[flash3780]

Consider whether it's truly necessary to press your pin into a blind hole. Through holes are easier to manufacture and allow you to get the pin out if something breaks, bends, or otherwise goes wrong.
Beyond that, you'll want to locate the holes with basic dimensions relative to datums with a positional tolerance with an MMC modifier and a projected tolerance zone over the length of the fastener. That should make your stackup work.
As for allowable tolerance? It's hard to do better than a positional tolerance of .010"dia on pins. You may discuss it with the manufacturer if you need to hold it tighter than that.

 

[CheckerHater]

David,

Looks like your question should be brocken down to sub-problems:

1. Can you buy the pin? Yes, there is a variety of standard pins out there. From what I could see you are looking fot "tight" fit, so spring pin will probably not work.
Your next choice is Dowel pin, made to variety if standards: ANSI B18.8.5M, DIN 6325, DIN 7979, ISO 2238, ISO 8735, etc. regarding of your location. All of these standards generally agree that dovel pin is made "oversized" to m6 tolerance.
Unfortunately m6 is not on the ISO list of preferred fits, so you have to rely on "industry standards" to fit your pin.

2. How to fit the pin? It is customary to press fit your dowel pin into one of the parts ant to have transitional "slip fit" for easy assembly with the other part while maintaining accuracy.
The recommended "press fit" for m6 pin is H6, so your H7 hole is very close. The "slip fit" would be F7, I guess this will have to go into your table.

3. How long the pin should be? It is the good rule to engage at least one diameter worth.

Like any other advise take it with the grain of salt. I have no idea what your machine actually is, like everybody else on this forum.
You are the one to make final decision.

Good luck!

 

[davidrdguez]

Hi everyone!

Sorry for the late answer. I was away from office working in a prototype we are building. It's nice changing from time to time.

I apologize for not explaining further what this project is about.

We need to place some nests (

http://img152.imageshack.us/g/02112010259.jpg/

the big one, the pin hole is at the bottom) where we put retro balls (

http://www.plxinc.com/pages/ball-mounted-hollow-retroreflectors-bmrs.php).

We use this to align very accurately our machine. Surveying this targets (the retros)

I found in the Catia V5 library standard pins; ISO2338 parallel seem nice.

I will try also the make hole instead of blind one.

Thank you all! this really helped!

David

 

[TED7]

Quick note with the hole, a good practice we use at our place is to always create a stepped hole, essentially a blind hole to the size required for the location pin, then a smaller through hole for sticking a punch though to remove it. This way prevents the dowel being bashed in too far by an enthusiastic hammer operator but also allows easy removal.

We use DIN 6325 almost universally on our gauging parts.

 

[KENAT]

Also, I've heard tales of pins popping out from the pneumatics of the trapped air, another reason for through holes when possible.

Posting guidelines faq731-376

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

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