What is stronger UNF or UNC

[JimM]

Hi Guys

I've built a hub puller similar to the one shown here

http://members.visi.net/~kohout/hubpull.html

The puller is bolted to the hub and then the screw tightened which pushes against the central shaft and leverage separates the two parts.

The first hub came apart no problem but the second one is proving to be a right bugger (This is a notorious problem with Spitfire hubs) In the end the threads on the nut/bolt gave out. I'm going to rebuild it but will a UNF or UNC thread work better in this application ?

Cheers

Jim

 

[malcolm]

Fairly sure UNC and plenty of oil is the way forward there. The UNC has more root area to the thread over a given distance so there's more metal to shear off.

 

[Reprobate]

I would advise a high carbon content bolt, normaly balck in colour. I would also use metric course as they are easily available. UNC/F are harder to come by these days.

 

[JimM]

Thanks for the advice guys coarse thread it is.

Only went for UNC/UNF as I have a tonne of them in fairly industrial sizes (another Ebay fit of madness !!)

Cheers

Jim

 

[oddball90]

Most pullers that i've used are a fine thread, which would help with the gearing. As to which is stronger, i would say fine thread, you will get more threads per set depth of steel. Hope that doesn't confuse to much.
Don

 

[lovelectricity]

hi there
fine could be better sure the one i made in college was about 22mm dia with a pitch of 1 - 1.5mm, it was a long time ago. it would however make pulling easier due to the pitch of the tread.

 

[rtbcomp]

Most pullers that i've used are a fine thread, which would help with the gearing. As to which is stronger, i would say fine thread, you will get more threads per set depth of steel. Hope that doesn't confuse to much.
Don

Yup - I'd go along with that.

Look at the thread as a ramp, it is easier to push a weight up a shallow ramp, which is the same as a low torque produces a high force in a fine thread.

I would say the fine thread is stronger because it doesn't go as deep into the stock as a coarse thread.

 

[Rusty]

Yup - I'd go along with that.

Look at the thread as a ramp, it is easier to push a weight up a shallow ramp, which is the same as a low torque produces a high force in a fine thread.

I would say the fine thread is stronger because it doesn't go as deep into the stock as a coarse thread.

 

[cobminor]

For your application go with UNF, much stronger on an extractor. There is not so much of the load on each thread, so less likely to strip off.

 

[Hitch]

UNF, more tpi, so its spread over more teeth. Plus it will be easier to turn.

 

[JimM]

OK you've convinced me UNF it is. I used a UNF originally as my own logic went along the same lines as the 'ramp' theory, I'll rebuild and give it another go

Cheers

Jim

 

[Reprobate]

Have been reading that apparently UNF is used for high torque applications, also this page may interest you as it shows standard bolt markings which should help you identify at a glance bolts made give the highest tensile stengh. Hope it helps.

http://en.wikipedia.org/wiki/Bolted_joint

 

[piman]

Hello Jim,

sounds like a similar job as on a Triumph 2000\TR5 or 6 rear hub, those tapers can be really tight. Did you use a big hammer to shock the taper once you had tightened the puller?
I also go for the fine thread but a standard nut is not really deep enough, you need, ideally twice the depth of a nut.

Alec

 

[JimM]

Hi

Yes did give it a few good thumps with a hammer but it was stuck fast.

Think one part of the problem was that the top plate wasn't thick enough, it was only a few mm thick and started to buckle under the strain. When I rebuild the puller I'll double up on the thickness there, unfortunately I'll have to stick with a single nut for the threaded section as I haven't got the facilty to tap out something that big.

Cheers

Jim

 

[rtbcomp]

The correct way to use a puller is to screw it up tight and wack it with a hammer on the end of the thread just once, tighten again and repeat.

Even if the fit is parallel as well as tapered.

 

[piman]

Hello Jim,

the puller I use has a 1\2" thick plate, anything that is a bit on the weak side diminishes the puller's effectiveness.

Alec