[Adobe Machine]

New project...I want to use aluminium timming gears on my new lathe retro-fit project to reduce inertia at the ball screws. Will need a series "L" x 3/4 inch, with a minimum of 60 teeth, plain bore( I will bore to my specs).Seems that all I have found on the internet is cast steel . Most likley I've just missed something obvious ? Any members have contacts that stock aluminium timming gears ?
thanks a lot

Adobe (old as dirt )

[fkaCarel]

60 teeth is a large one. My book says OD 181.81 mm at 2.59 kg. These sizes are normally cast with spokes. So maybe if you compare the specified weight to an aluminium blank, it's not so bad after all. And there is always the option of removing excess material at your own risk.

[Adobe Machine]

That is correct, but with the steel hub, the assembly gets real heavy.Drilling excess may be my only option if I can not find a lighter set.Making my own on the cnc mill is the other option, just talked to our local tool grinder and he can grind a 3/8 carbide end mill that will match the pattern,and I have a chunk of 6061 8" round I've been saving for "something"...but that is a long ,drawn out PITA to mill.
Thanks for the reply.
Adobe

[NC Cams]

You can "web" out the center so as to make it in the cross section shape of an I beam. One piece but lighter.

Keep in mind that aluminum is lighter but NOT as rigid or wear resistant as steel or cast iron - especially if it has to rub against a dissimilar harder material.

You can also make a hub/web out of aluminum and cut out the hub/web of the iron/steel gear and then bolt the two together - ferrous teeth, light aluminum hub/web.

Adjustable timing sprockets for automotive use are done this way and work just fine.

[Adobe Machine]

Thanks NC Cams,I decided to make both large gears. I just got back from our local tool grinder and he made 3 carbide end mills with the correct pattern very economically.I alredy have the material , so the only thing standing in my way of finishing is getting off my bu__ and make it happen.
In so far as wear:there is no metal to metal interferance, RPM at the large pully will not exceed 400 rpm ( in G00), most likley operate at 100-200 rpm, I always use 2 tensioner / guide wheels to get the correct belt angle on the smaller pully. I would estimate the arrangement will out last me, then my kids can figure how to get rid of my stuff.
Yes, we use gilmer/steel alumnium on both the cam drive and blower drive ( 14:71 @ 30% over) on our 540 cid blown alcohol motor, I can not remember a failure ( except lots of blower belts) of any of the gilmer pully's, my small block street rod is used every day ,I do not see any wear on the blower pullys or tensioners...( 30,000 miles).
I would use 7071 if we did not alredy have the 6061 as I understand the wear factor on that alloy is near heat treated steel ?
Will lighten the alum. pullys also...Do you think possibly a hard anodise would help any wear issues?
Thanks for the reply
Adobe (old as dirt)

[NC Cams]

Small symantics problem here that leads to mucho confusion.

Vee type Fan belts use pulleys.

Timing belt drives that utilze Gilmer cogged or HTD style belts (ala Jesel timing belt drive or blower drives) use sprockets.

Gears involve metal to metal contact for direct transmission of forces from tooth to tooth via direct contact.

Many folks use "timing gears" incorrectly in mixed mode when the say something but mean something else. Ergo, the source of major confusion and misunderstandings.

My caveats pertain and remain in effect with gear drives - your experiences pertain to timing belt drives (which do NOT incorportate gears in contact with belts).

[Adobe Machine]

Yep, your right about symatics...have seen lots of expensive projects go south due to one engineer misunderstanding anothers "jargon".Here's one " Trapezoidal tooth timing belt pully" ( meaning a gilmer style " sprocket ").Some catalogues use " sprocket" or "pully" or "gear" all referancing to the gilmar style drive...Anyway, next question: do you think hard anodising would be necessary at all ? Low stress, low rpm situation ?
Thanks

Adobe ( old as dirt )

[NC Cams]

Don't forget the motor versus engine juxtaposition, too.

We had aluminum pinion gears (gear gear) that ran against nylon spur gears in our R/C cars. The hard anodized ones from Delta were jewelry and hardly ever wore outside of off/road dirt applications where EVERYTHING wore.

The color annodized or non-annodized onces always wore quite readily in comparison.

Yes, if you qualify the situation with the right words, anything will live. However, in real life, the fortified and properly machined ones always seem to work better/live longer.

Words versus actions - which would you rather choose/rely upon????

It is purely a matter of education and discipline that results in people using the right terms in discussing gears, sprockets and/or pulleys.

Sadly, the allowance for the "close enough, you know what I mean" philosophy of education has led to the dumbing down of society.

I used to think it was cute to say "give me a wrench - what size? Don't care I'm going to use it for a hammer anyway" until the fateful day a maintenance guy I worked with at a construction company went BALLISTIC. A 20 minute dissertation followed after which I used the phrase MUCH more carefully and judiciously. Illustrates the point, however, at how dumb you look when you use the wrong terms.

[fkaCarel]

Will need a series "L" x 3/4 inch

This qualifies for a timing belt drive. If you make the pulley yourself, you will see that smooth, backlash free running is determined by outside diameter, tooth shape and tooth bottom. In my experience it's precision work. Wrong dimensions can lead to load-related backlash. Hard anodising can change (grow) dimensions. So if you make your proof of concept pulley, it is changed by anodising. Your local anodiser can advise on this. With the rpm involved and keeping in mind the diameter of this pulley and non grinding concept of a timing belt, I would'nt do it, although it absolutely improves the appearance!

[NC Cams]

WHenever you do post machining heat or surface treatment, you MUST take growth/shrinkage into account along with net surface finish smoothness.

In the afore mentioned gears, they MIL spec hard annodize ones simply didn't wear. The "gold-red-green-purple" foofy color coated ones did.

We have some uncoated belt sprockets on some equipment -they all show wear from the belts as they squirmed into/out of the sprockets over time.

Outside of steel sprockets, the only way I know of to prevent wear on aluminum sprockets is to hard annodize them, providing you compensate appropriately for growth/shrinkage. Don't forget to tumble in ultrafine media afterwards - you need to make the coating glass smooth or else the aggressive texture of the H/A will tear up the belt.

Keep in mind that the aluminum oxide formed via H/A is the same stuff they use to make "sand paper". Need I say more???

[Adobe Machine]

Glad this is a just "hobby"..Just finished the first one (PITA, have 3 axis, not four , had to index all 60 teeth) after deburr looks ok, and mic'ed to specs ( I used a steel one to compare),glass beaded and will take to local plating company for hard annodise tomorrow.
Another comment: I had to disassemble a Webb Mill ( Bridgeport copy) head a few months ago as it had gotten noisy...This Mill dates to 1981, never been apart before. The back gear drive is gilmar, L ,3/4 " and the large pully is in fact alum., Very little if any wear in the teeth,some wear in the shaft diameter ( rocking) due to the fastner being loose..this machine has lots of hours on it.This gives me some confidence in the wearability of 6061 T6 for a timming sprocket ( pully, gear etc )Thanks for your comments.
NC Cams, I'm copying from a cast steel gear,and I just have to tell you this is not a precision piece ! From the inner bore to O.D. there is a variance of .006 to -.002.. hope mine is better than that .(at least mine is +.0008-.001 )
And FKACAREL, yes that is precision work,no fun,bo-o-oring kinda work .You just have to admire those old time machinest who stood in front of a mill/lathe for hours ,EVERY DAY , doing this kind of work !

Adobe ( old as dirt )

[NC Cams]

If you ran a belt driven cam sprocket with 0.008" TIR in an automotive timing, you'd spit belts off like crazy.

When we grind the register for the timing sprocket on cams, we hold TIR to under 0.001", more often than not, under 0.0005" TIR.

It's amazing what passes for "precision" in some industries.

Perhaps in machine tools, 6061 wlll do just fine. My durability requirements relate to belt drives for production camshafts in OHC systems. Far more abusive and highly stressed environment (heat, cold, dirt, debris, oil seepage, etc).

[Adobe Machine]

I can see that durability in a cam sprocket must be 100%, especially with the spring pressures and lift they are using now, plus a lot of setups drive BIG mechanical pumps off the front of the cam, which at rpm cause a lot of drag.Just courious, how much "flex" is in a camshaft driving .950 lifts (+)have ? When grinding the profiles, do you compensate position on say # 8 lobe as to # 1 lobe ?In the years past we would break cams in half pretty regular ( nitro motors), but see less of that now, must be due to better machining and heat treat ?
thanks, will post specs on the sprocket ( pully, gear ) when its back from plating.

Adobe ( old as dirt )

[NC Cams]

Re: cam flex = keep in mind that the cam flexes in both directions - opening side and closing. We do not put 'twist' in the cam to compensate for flex. More importantly, none of the race blocks run stock size cam bearings.

8620 and other "traditional" steel roller cores won't hardly last 200 miles in a Craftsman truck motor. Cam cores are now tool steel in some instances - cast iron was eclippsed as being viable nearly a decade ago. NASCAR 'Cup is at 55mm needle bearing journals with 60's on the horizon. Drag blocks (pro stock) are at least 60mm.

Since the torsional stiffness increases with the diameter to the 4th power, a small increase in base circle diameter (with an ensuing barrel diameter increase) does wonders for stiffness.

OEM cam sprockets are all powder metal anymore. NO aluminum outside of the glitzy "tuner market" stuff. Jesel stuff is good but the Cup boys don't run it more than a race (700~1000 miles).

The nitro boys are brutal and only use bigger mortars when someone comes up with something that purports to be bulletproof....

[Adobe Machine]

Thanks for the insight to your industry, very interesting CNC machining applications......Nothing is bullet proof in Nitro..still have 6, 500 inch KB blocks with lots of "windows"..horrible but fun waste of money !.

Adobe ( old as dirt )

[FPV_GTp]

New project...I want to use aluminium timming gears on my new lathe retro-fit project to reduce inertia at the ball screws. Will need a series "L" x 3/4 inch, with a minimum of 60 teeth, plain bore( I will bore to my specs).Seems that all I have found on the internet is cast steel . Most likley I've just missed something obvious ? Any members have contacts that stock aluminium timming gears ?
thanks a lot

Adobe (old as dirt )

Hi

just a thought , have you had a think about using 4 cylinder overhead cam gears that are tooth belt driven arrangment , they are light and strong , not aluminium but they a profile milled with slots and holes to make the gear lighter . A lot of japaness cars have them.

and if you use the matching crankshaft gear the ratio is 2:1 , if you get hold of some and have a look at them and get some aluminium and machine and cut the teeth copying the engine dimensions and make the center mount holes what what ever specs you need them . Wouldn't take long to make .

cheers

[Adobe Machine]

Thanks for the idea FPV GTa...as a matter of fact I looked in an automotive timming gear ( sprocket, pully ) catalogue and ended up copying some of their lightning procedures when I milled my first gear last week from 6061 T-6. The weight difference between the cast steel gear ordered and the one I milled is a lot by"feel"( I do not have a scale sensitive enough to weigh the difference).I believe it will help eliminate the "flywheel" action somewhat.My old brain cannot remember the formula for predicting inertia in a round object,and the old text books are in "deep"storage in the garage.
As soon as the 1st gear is back from plating and measured, then will mill the 2nd one .
Thanks

Adobe (old as dirt )