Large diameter washers and hole+bolt sizes ?

[Kall545]

Hi
What size large diameter washer can I use with which right hole+bolt combination without bending/deforming the large washer ?

I'm talking about those small hole washers that have large outside diameter and tend to bend/turn conical when used in too large holes...and wondering what is the right size washer+hole+bolt combination to use without deforming the washer ?

I have a bolt size 8mm and hole is 14mm so which washer size do I use 16mm or 24mm ?

 

[tbuelna]

Is a smaller diameter hole out of the question? Or how about a hat bushing with a height that provides the required clamping without excessively deforming the flange? If a plain washer must be used, it needs to be thick enough to safely handle the fastener axial preload without permanently deforming. Use a thicker washer, a smaller diameter hole, a bolt with a larger flange diameter, or some combination of these.

 

[drawoh]

KalleBoy,

You are going to have to work this one out. Roark's has equations for flat round plates. You can figure out the screw torque and the washer size.

--
JHG

 

[boo1]

bushing or use a double washer stack

 

[Screwman1]

How much clamp load are you going to need on the bolt? That is one part of the question here. How thick is your washer and what hardness is it?

 

[drawoh]

KalleBoy,

Take a look at the Belleville washers in the McMaster Carr catalogue. They have some serious, heavy duty ones, unfortunately, without technical specifications. I worked out their stresses and compression forces, and I found that they approximated the yield strength of the screws. This did not suit my purposes at the time, but I made a note of it. This could be useful sometime.

You will have to look them up and do the analysis, and you may have to use a torque wrench to assemble everything. This may solve your problem.

--
JHG

 

[MikeHalloran]

Fender washers are not intended to carry large axial loads.
If you need something stronger, it will have to be custom.

It does not have to be expensive; it's possible to bang out a rectangular plate with a hole in it, in just a few seconds with an ironworker, provided that you don't use stupid tolerances.



Mike Halloran
Pembroke Pines, FL, USA

 

[LittleInch]

You should not be having a nut which is the same size or smaller than the hole.

What is needed is a plate of the same thickness as the base plate the hole is in welded to the plate then droll a smaller hole.

Trying to fudge it with a washer is just asking for trouble IMHO. If you search for washer on this forum you find some interesting debates and lots of people mention asme PCC

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dvd]

Try looking at the Specification for Structural Joints Using High-Strength Bolts. The following table appears within and provides a lot better starting point.

 

[BEMPE16524]

Any reason why can't use bigger bolt?
I would just make a combination of bush and washer if you can't use bigger bolt.

 

[Kall545]

It is a large heavy sheet metal plate that needs extra assembly clearance.
- Company apparently has only M8 size screws ?

 

[Compositepro]

I think that the shear line through any washer from the OD of the bolt head to the ID of the hole should no exceed 45 degrees. Otherwise the washer will be prone to cupping.

 

[LittleInch]

Thinking about this a bit more I think you really need some sort of insert, kind of T shaped in cross section with a hole in the middle. The depth of the tee is up to you and whether you tap the hole and screw it in is up to you or just use the flat section to take the load into the plate.

The extra depth of the lower T shape provides a lot more strength than a simple flat washer of variable strength.

There is no way you can accept having a flat plate / washer start to bend - you're then already at max force and any more force will get worse and worse as the bending continues.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Tmoose]

Hi KalleBoy,

are you saying you need the full 14 mm DIA holes to assemble the components ?

 

[ameyerrenke]

Does the bolt need to be a socket head? A standard hex head bolt or a flange bolt would help your situation considerably. I assume there is not much load going through this connection.

 

[ornerynorsk]

Not to be judgmental, but 14mm holes to ease assembly for 8mm bolts is just plain sloppy, and it causes other problems that other posters have mentioned. Are these hand-made parts, or is any kind of machine control being exercised in the manufacturing of them?

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.