pin for misaligned holes 2

[Gore]

Having two steel plates 0.5" thickness with 3 holes each and misaligned within the tolearnce 0.046", which kind of pin should I use for them? There is a torsinal moment between the plates.

 

[rb1957]

if this is a real structural application ...
(where people's lives are at stake) ...

i'd suggest opening up the holes to the next standard size.

if your bolt diameter is fixed (by something you're bolting onto the plates), then bush the holes

no more "risky" approach would be to install clearance bolts (the largest bolt to fit into the misplaced holes). this is riskier because you're relying on friction (to an extent), and because the plates "could" move relative to one another. (the first solution virtually prevents any relative movement between the plates because there are no clearances.)

this'll be smaller than your BP fastener, and you should be confident that it is ok.

when you say the plates are loaded by torsion, do you mean that the bolts react with in-plane shear, or are the bolts loaded in tension ? (this tension load would actually carried by the joint compression forces due to the bolt preload ... what sort of preload were you planning ?)

 

[CESSNA1]

GORE: Follow the advice of RB1957. You could also use offset dowels or ream one or more holes larger and use step dowels. The real issue though is why are they offset, If the application is critcal the holes are usually drilled and reamed together. Is this one of a kind or is it production. What kind of load do they see? Are the dowels only for locating and other devices carry the load or do the dowels carry the load?

Regards
Dave

http://www.wsec1.com

 

[GregLocock]

I'd use a dowel pin in one hole, and bolt the other two, in production.

On a production car there are virtually no bolted structural joints that would maintain integrity in the absence of friction, so I'd have no qualms that a properly designed bolted joint would cope.

The dowel pin is there as nicety, it could be a bolt as well.





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Gore]

The two plates are connected by 6 bolts. I cannot modify the dimensions of the bolt and increase the clamping force between the plates. I am wondering that the tortion aplied to one plate will overcome the friction. For this I want to add 3 pins. Unfortunately I do not have room to drill holes when the two plates are installed. In one plate the holes are already drilled and I cannot change them. I want to drill holes in the other plate separetelly (12mmm or 16mm, I have two different applications).
Inevitably I will have offset between the matching holes.
Maybe offset dowel pin is a solution. I don't know how to install them, and I don't know a supplier for offset dowel (metric). Are offset dowels sold in sets? I suppose that during the instalation the necessarily pin is selected depend on the offset between the holes.

 

[rb1957]

i think CESSNA1 was talking about making your own dowels, out of bar stock. i wonder about the strength of such a dowel, it obviously can't be as strong as the BP bolt.

can you enlarge the holes to encompass the offset holes + some, install a plug (suggest shrink fit), then drill out at the correct location ? possibly you can't because of edge distance issues.

i don't think you count on friction between the plates for carrying much load, count on the torsion being reacted by the bolts in shear, so you need a good fit (between the bolts and the holes).

it sounds like you have one plate drilled off, and are planning what to do if (when) you get a mismatch witht he 2nd plate on ass'y. this off, this should have been considered by the original designer, as the holes are not match crilled there will always be some tolerance for mis-match; so what does the drawing say ?

the two plates are oriented to each other somehow in the ass'y. can you align the plates in the ass'y, clamp them together, then drill out on the bench ? if you can do this, next time (if there is a next time) only drill a pilot hole in the first plate, this way you'll get match drilled holes (when you open them up later).

 

[GregLocock]

rb, in a properly designed bolted joint NONE of the load needs to be taken by direct pressure of the hole on the shank of the bolt, it is all taken in friction. Bolts use clearance holes.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[rb1957]

guess that depends on your experience and industry

 

[Tmoose]

This page shows commercially available offset dowels.
Used for repositioning things like camshafts to change the cam timing and bellhousings to center transmissions.

http://69.20.110.81/index.asp?PageAction=VIEWPROD&ProdID=62439

You'd have to separate the plates to install them. And would probably need to add some more holes to bolt the plates together ?

As far handling torque with friction, flywheels bolted to crankshafts seem to be the modern day standard.

http://www.streetsports.com/Photos/Vehicles/Honda-Acura/Integra GS black/Integra Images/flywheel.jpg

 

[IFRs]

I think you can match the holes, if you put the first plate on a milling machine baed and indicated each hole center. Then put the second plate on the milling machine and drill at the same X-Y coordinates. A good machine shop should be able to do this for you. In other words, I question the assumption that "Inevitably I will have offset between the matching holes". If you work on that side, you can solve your problem. Don't accept the ideas that you can't locate the holes accurately enough!

 

[diamondjim]

Is each hole .046 out of true position?
I think you could use one of the dowel
pin holes on each part as the reference
datum hole and taper ream the other two
holes with the plates bolted together.