Ask an Engineer

[carburator]

single point broaching a lathe is a quick and dirty way of getting ones ass out of a hole and also very effective.

you can do the same in a mill with a rotary table with less hassles ( powering the table up and down is cheating )
HSS is fine, just take you time with the tool grinder ( or if you have a water pump drown the bugger )
otherwise couple of passes and leave, don't get color run though in your application whats a couple of rockwells..

generally we have worked out number of splines then ground a three point ( triangular broach end on ) to provide
full support or equal stress to stop the little buggers from wandering off... genrally we also stick a lead on them
and provide a decent releif area for swarf to curl up in ( and a cutting edge )

[bogan]

A painting question this time, I do a bit of cosmetic milling, which often involves graphics set into the part by a mm or so. I want the graphics to stay as a metal finish while I paint the rest, can I fill that area in with something fluid like wax to mask it off for painting?

[Ocean1]

Dunno. The only time I've done it I just scraped the paint out with wee toolmaker's files.

What I have done is waterjet cut graphics from 2mm sheet and epoxyd them to the housing for a positive relief effect.

Well, I was positively relieved after the earlier effort.



Sorry.

[AllanB]

Would you not paint first them cut the graphics in?

[bogan]

Could do, but it means setting up the work again, and the finish on the bottom of the cut need a polish anyway, which is easier to do without worrying about taking paint off the rest of it, and probably a similar amount of work as removing paint anyway.

[BASS-TREBLE]

Why not paint it with a roller? It works as long as you don't drown the roller with paint to the point where it drips into the cavity

[nodrog:Me]

A painting question this time, I do a bit of cosmetic milling, which often involves graphics set into the part by a mm or so. I want the graphics to stay as a metal finish while I paint the rest, can I fill that area in with something fluid like wax to mask it off for painting?

Fill it with plasticine or bluetac, then just blow it out with compressed air after paint is dry.

[bogan]

Quick question re greased bushing materials, aluminium on steel is better than aluminium on aluminium right? This one is for a rear brake torsion bar, so no force when it moves (only moves when you adjust the chain/wheel/brake position), but plenty of force when stationary.

What about galv pipe, better to have it on steel or aluminium? and if steel, is it by much? This is for a cart, approx 200kg load through 4 wheels on 2 40mm galv pipe axles, expected to move less than 100m per year.

Both of them are low speed low use applications so not worth doing bearings or bronze. In other news, I turned up a very nice 60x90x80 bush for the vertical spline shaper out of bronze last week, cuts bloody nice, but hot chips everywhere!

[Ocean1]

Quick question re greased bushing materials, aluminium on steel is better than aluminium on aluminium right? This one is for a rear brake torsion bar, so no force when it moves (only moves when you adjust the chain/wheel/brake position), but plenty of force when stationary.

What about galv pipe, better to have it on steel or aluminium? and if steel, is it by much? This is for a cart, approx 200kg load through 4 wheels on 2 40mm galv pipe axles, expected to move less than 100m per year.

Both of them are low speed low use applications so not worth doing bearings or bronze. In other news, I turned up a very nice 60x90x80 bush for the vertical spline shaper out of bronze last week, cuts bloody nice, but hot chips everywhere!

Yes.

General rule for bushes is no longer than 1.5 x dia, material almost doesn't matter for that duty but consider cast iron on galv pipe. Worth noting that some materials cold weld, aluminium on aluminium will. The zincon pipe is OK, but make sure it's reasonably cylindrical and keep clearances around 0.05dia.

Yes, bronze makes for little sharp fuckers down your shirt. What bronze?

[bogan]

Yes.

General rule for bushes is no longer than 1.5 x dia, material almost doesn't matter for that duty but consider cast iron on galv pipe. Worth noting that some materials cold weld, aluminium on aluminium will. The zincon pipe is OK, but make sure it's reasonably cylindrical and keep clearances around 0.05dia.

Yes, bronze makes for little sharp fuckers down your shirt. What bronze?

Thanks, not sure what bronze, just found it in the corner of the workshop, and it was the perfect size...

[bogan]

Question about fire extinguishers, my insurance says I have to get one for the shed and it needs to be serviced yearly, does that mean I have to buy one with a service contract? or just take any old one in to get serviced?

Any recommendations on places/types/brands?

[Akzle]

recommend steer clear of bunnings 1lt specials.

your insurance company should be able to specify minimum requirements. for vehicles it is class B 1.5kg, sometimes two of, depending what you plan on driving into.

for practically putting out a fire, you're probably going to want a powder one (class B) although, depending on what's more likely to catch fire, a co2 may suit. (and doesn't make a helluva mess)

and probably a 3kg+ size. needs to be mounted with easy access on an exit route. (bench height by the door, normally)

"servicing" can be done at anywhere that services em, on any extinguisher. phone your local fire station to find place local to you.

[Ocean1]

Question about fire extinguishers, my insurance says I have to get one for the shed and it needs to be serviced yearly, does that mean I have to buy one with a service contract? or just take any old one in to get serviced?

Any recommendations on places/types/brands?

Does the insurance company specify what type of extinguisher or are they just padding the contract with escape clauses?

Either way you don't have to buy a service contract, but if they're calling for an annual service it has to be done by a "qualified person". Be aware that there's lots of them driving around looking for work, offering to check your extinguishers free and service them cheaply, (just sign here, sir). I know of one warehouse that was signed up to three different contracts, and unsurprisingly the service agents had completely ignored each others tags, in some cases refilling extinguishers last filled a month ago.

Type of extinguisher depends on likely use but in most workshops I'd expect to see ABE dry powder items. As for price, no real suggestions, walk the fingers.

[BoristheBiter]

[COLOR="#139922"]
ali is soft, so anything harder. carbide / HSS are brittle, not so good under a press.
ideally something pre-splined. i can't think of anything 8mm pre-splined.
get some 8mm mild steel bar, get busy with needle file (or mill and rotary-indexing table if u have),
then case harden it.

That's why most are made from HSS.
What a nob end.

[husaberg]

Right not everyone knows this but all the late era MV Augustas (the Real MV's that finished in the 1970's) actually had aluminium alloy disk brake rotors.
I know many have experimented with plated and plasma coated aluminium alloy disk rotors without success.

MV supposedly had no trouble with the plain aluminum alloy rotors but what alloy might they have used and what sort of pad material would be suitable.

yes i realise an MMC material would be probably better but does anyone have any ideas?
I are picking that it would have to had a high silicon content....