What grade of aluminium is best for making a pulley?

I have, at long last, run out of my hoard of Picador pulleys. So I need to make some.

What is the recommended grade of aluminium?

Andrew.

Any of the 6---- or 7---- series would do they are much better to machine than the pure stuff.

6082 is my go to grade. nice to machine

Thanks guys, I shall get some on order!

Andrew.

Hi Chris

I usually end up with a birds-nest of swarf when taking light cuts but the chipbreaker does work better with deep cuts, this is using ground inserts, HSS or diamond tipped don't perform any better.

What's your secret to machining 6082 ?

Emgee

Edited By Emgee on 02/04/2023 18:38:23

How critical is the application in terms of load and RPM? Aluminium pulleys are usually cast, not fabricated, because die castings are less likely to burst. And if the pulley will be worked hard, or take snatch loads, the alloy needs to be tough enough not to fail at the shaft fixing.

No problem making small diameter slow RPM pulleys from 6082 stock where the stresses are low, but I'd buy the commercial product if the pulley was to be spun fast or heavily loaded. Big stress difference between a 3" pulley fitted to a 1000W lathe chugging along at 600rpm, and the same item pushed over 6000 rpm by a 50kW car engine.

A genuine Picador pulley is probably significantly stronger than a home-turned copy.

Dave

If the rpm is critical, then 7075 T6 would be strongest easily available. But the 6082 would be far superior to those ancient Picador cast ones.

I think Picardor pullets were mazak, not the strongest material known to man.

A pulley from 6082 T6 would be my preference over an unknow commercial one, tensile strength of the bar is 50 to 100% more than typical cast alloys. One only has to look at those chipped pullies that we see here from time to time to see another disadvantage of cast ones

Edited By JasonB on 03/04/2023 07:30:21

Machining 6082-T6 with "GT" inserts seems to go well with a spray of suds oil to prevent build up on the tool. Birds nesting of swarf is the nature of this type of material, I tend to stop the lathe after every pass or two and clear the area.

and For 6082, need a geometry with a short chip breaker. It will curl with a light cut, but a deeper cut like 2x the tip radius and a feedrate of 3/4 of the radius to the radius per rev. So a 0.2mm radius , 0.15mm/rev to 0.2mm/rev, and cut depth of 0.4 Ø0.8mm cuts. Peck the cuts if it starts bird nesting. So hand feed and stop every .5mm of travel if the tools you have do not make curl chips. I use a kyocera CCGT09T302MP-CK PR1725 or PR1425 grade. I have them in the 09 and 06 sized inserts to suite the boring bars and the external holders.

For getting down into the pulley sides there are some very high rake 35 deg inserts like the VCGX110304 in the 0.4mm radius is the more common in these, but Iscar make a very good insert that is in the 0.2mm radius and also a very high rake for aluminium and plastics.

Several people have stated that a high speed pulley will need a very strong material. It's worth doing some sums. This is not going to cause me any sleepless nights, less than half a ton/sqin. It's not surprising really, at the other end of an IC engine is a much larger flywheel, which is made out of a much denser material which seems to survive OK. In case you feel like exploring further note that some sources use the reciprocal of Poisson's ratio, so instead of (1-u) they have (1-1/m), which causes a bit of confusion.

Edited By duncan webster on 03/04/2023 13:49:28

I did take Dave's warning with a very large pinch of salt. So thanks Duncan for the supporting calculation!

Andrew.

Dave warns against 'fabricated' pulleys, but what exactly does he mean by it? To me, fabricated implies a built-up structure - the Forth Bridge is fabricated from steel tubes and rivets. But the pulleys we need (I think) are one-piece, whether cast or forged or turned from an extrusion.

Experts always know what they mean, but they need to remember that we are not all experts at what they are expert at.

Regards, Tim

On the subject of pulleys, I've just turned a couple of pulleys, about 30mm diameter and picked out a bar of 30mm 'aluminium' from my box of bits. I don't remember where I got it or the spec. I tried to clean up the end of the bar with it centred up and I kept getting that chi, ch, ch noise every rev - just like it was off centre. I carried turning down and couldn't;t get rid of a patch of crystalline looking stuff. Looking at the end of the rod, that whitish region went down several mm. I tried different tools but same result.

Is this a common problem? It's of no consequence for my inconsequential project but it was interesting. I guess you'll all tell me to use Metal For U to source my stuff. fair enough but eBay is a convenient source of one-off bits with no postage and the pukkah sources have a minimum quantity etc. etc.

Same problem with some cheap steel plate; drilling one particular hole gave graunchy noises and chewed up the drill ends. Snatched at the pilot drill and I feared it would break. Seven other holes were no prob. (I used cutting oil, a pilot and fast speed).

The scrap bins in the raw material stores where I worked always had some cut off ends of bar stock in them. They were cut off and discarded due to the inclusions in them. As the stock is cold formed the ends curl over towards the centre and in the worst cases some of the rubbish on the end face ends up being squeezed into the material where it is hidden. These discarded ends were usually in the region of 100mm long to be on the safe side. A stockist who is cutting off parts and sending them to a customer does not want the cost of too much waste so would probably cut off the minimum to remove the curled over end and no more. The result is if you get the first piece cut off a length of stock there is a risk of the end face scale and corrosion being embedded in the material to a significant depth.

Martin C

Hi Martin

Thanks. That makes sense. No problems for me in they case but a 'proper job' needs a good supplier. I'll see what the rest of that bar holds for me. The other end may be fine.

Andrew

"Inclusions". I know that term from jewellery.

.

I suspect that Dave just meant ‘fabricated’ to mean ‘made by machining’ … but only he can confirm or refute that.

It is, however quite possible to fabricate Vee pulleys by using two truncated cones … either fixed together or keyed, with an adjustment mechanism.

MichaelG.