BZP strength

[JimM]

Hi all

I need some M6 threaded bar for use in clamping bits and pieces down on my milling machine. Screwfix have various bar listed but don't give any indication of tensile strength etc If it's listed simply as BZP is this likely to be 8.8 ? Also is BZP stronger than Stainless A2 or A4 ?

Steel
http://www.screwfix.com/app/sfd/cat/products.jsp?id=29072&ts=44874

A2
http://www.screwfix.com/app/sfd/cat/products.jsp?id=72061&ts=44874

A4
http://www.screwfix.com/app/sfd/cat/products.jsp?id=32264&ts=44874

BZP
http://www.screwfix.com/app/sfd/cat/products.jsp?id=43605&ts=44874

Thanks

Jim

 

[bigbadbugga]

I would think it is just zinc plated mild steel.

 

[Hitch]

Studding is usually 4.8 if its not specified as 8.8.

BZP means its bright zinc plated, beares no meaning on the strength.


For clamping, i would avoid stainless, it tends to bind up easily if it picks up a bit of dirt on a thread. As to A2/A4 being the strongest, thats the level of corrosion resistance, nothing to do with strength.
They are generally grade 80 (800n/mm2) and smaller 8.8 steel bolt are also 800n/mm2)

 

[langy]

In my opinion studding is ok for garden gates and sheds, It has no place where quality fastners should be used.
I wouldnt use stainless for clamping on something like a Mill because of the galling issues it suffers from, much better to use a quality 8.8, 10.9 etc etc

 

[Pete.]

I bought some studding from Screwfix and the quality wasn't bad, but not the best. Should be plenty good enough for clamping on the mill but I wouldn't use M6, go for the thickest that will fit in your slots.

 

[JimM]

I bought some studding from Screwfix and the quality wasn't bad, but not the best. Should be plenty good enough for clamping on the mill but I wouldn't use M6, go for the thickest that will fit in your slots.

That will be M6 then !! Stupid design for a milling machine, it's on old Elliott Juniormill, table is 28" x 7" but the slots are tiny it will take 1/4" studs but nothing bigger. M6 is easier to source than 1/4" though

Thanks to all for the advice I'll look out for some proper HT studding, was just hoping the Screwfix stuff would do as there's a branch 2 mins from me

Cheers

Jim

 

[Pete.]

It'll probably be ok. Otherwise, how about buying an assortment of M6 or 1/4" 12.9 socket capscrews and brazing some fatter peices to the heads to hold in the tee-slots?

 

[hareng]

As above its Bright Zinc Plate i have a few lengths here. Its softer than 8.8 easily sawn and i would assume dont quote me its just a soft grade ms round threaded judging by the feel, possibly bright!
Luckily the M6x1mm thread is reasonably course, personally i dont think it will be ok unless removing thous, 20 thou no way.

 

[Dune]

Each type of steel has its own tensile strength, all dependant on treatment, carbon content, if its an alloy etc etc. If your just holding down a work peice on the mill bed you have to consider how many tie downs youll be using. If your going to hold it down in three or four points almost any steel will do.

Typical ultimate tensile strength (MPa) Carbon Steels 276-1882, Alloyed steel 758-1882, Stainless Steels 515-827 and tool steels 640-2000.

Now a megaPascal is equal to 1 Newton/mm2. So considering stress = force / area.
A 6mm diameter rod would be 28mm2 in cross section
therefore 28 times say 276 9lowest of the carbon steels) = 7728 Newtons.
9.81 Newtons is a kg. So 7728 / 98.1 = 787kgs of strain before breaking.

So any MS that you can get hold of should be enough to hold down an work peice on a mill bed. Now for safety you would divide by 1.4 for structures but the thread will actually give way before the bar snaps.

 

[Pete.]

M6 studding can hold 3/4 of a ton?

 

[chap]

The problem with soft 6mm studding is that you can easily over-tighten nuts and strip the stud thread.
Also, M6 (dia 5mm core) might be a little springy and bendy to use as hold down.

 

[langy]

Ditto, i certainly wouldn't use studding as hold downs on a mill, it stretches like ******y, very handy to be milling and have something fly off

For a few coppers more you could be safe.

The problem with soft 6mm studding is that you can easily over-tighten nuts and strip the stud thread.
Also, M6 (dia 5mm core) might be a little springy and bendy to use as hold down.

 

[Dune]

M6 studding can hold 3/4 of a ton?

That is the ultimate tensile strength, you would have apply a safety factor for each specific use, but yes. Consider say some 13mm nylon rope, you wouldnt think twice about towing a car with that and that has a lot lower ultimate tensile strength. But as I said the thread is the limiting factor.

Some of the new steel alloys we use in bridge design would be able to hold 10 times that for a given diametre.