Metallurgy blah

[schrodingers cat]

When you go to buy an 8.1mm drill you will wish you had just bought some rearsets. Drill 0.5mm oversize or look at imperial equivilents for a (possibly) tighter fit.

The trouble with CAD design is that it is very easy to design stuff that is impractical to make

[bogan]

The trouble with CAD design is that it is very easy to design stuff that is impractical to make

fuck yeh, and if you got a cnc machine to go with, you can end up with parts that have curves all over the place and look shit just cos you can doesn't mean you should, incidentally, anyone got any ideas of what to do with a 37cc V8 which has to much friction to run as a stirling engine?

[Mental Trousers]

That shits up to who I end up sending it to. I understand with most CNC mills it aint hard to do odd size holes so 8.1mm shouldn't be a problem.

Not having done anything for CNC machining (or any sort of machining) before I'm having to rely on advice from other people so any advice is very much appreciated.

[bogan]

That shits up to who I end up sending it to. I understand with most CNC mills it aint hard to do odd size holes so 8.1mm shouldn't be a problem.

Not having done anything for CNC machining (or any sort of machining) before I'm having to rely on advice from other people so any advice is very much appreciated.

yeh, easy as to do that in a cnc, is a well designed part for CNC'ing too, can machine it all from the one side (just do the countersinking afterwards) which in most cases makes it easier and cheaper to make. So many people (students) aren't aware of machining constraints when designing parts.

[Grumph]

Something as simple as these hangers don't really need to be done on CNC - you'll learn more about marking out and fabricating doing them by hand - and it'll be quicker in the end too as you won't have to wait for someone's CNC to come free.
An 8.0mm drill even in very good condition will drill a clearance hole for an 8mm capscrew, don't faff about with 8.1mm - not needed.

It's like the old story about the guy polishing Rolls conrods by hand - by the time he's finished he can tell if it's right or not...

[Mental Trousers]

Lack of a shed and appropriate tools means actually making anything is a problem. Besides, I want some cool looking ones

Rear sets are just one of the things I'll eventually have made. From the list of things I want to do they're the most urgent and among the easiest so they're the best starting point for me to learn how to design stuff for CNC machining.

bogan, thanks for mentioning that machining from one side is preferred. I wasn't aware that sort of thing was an important consideration.

[Ocean1]

Pretty pictures. Make sweeping generalizations.

Uses M8's and M10's.

What are you using to make the pictures?
The slotted hole at the base of the brake cyl mount looks wrong. Makes for a comparitively weak area at the bottom of the brake mount arm, I'd add some material to the sides to bulk up the cross sectional area.

I'd also radius the external corners and fillet the internal ones by p'raps 2mm, less stress raisers all round.

Fasteners that size are typically 2 - 3% undersize, so if the fastener is also doing duty as a locator then 0.1 oversize is good.

Could waterjet cut them from plate then munch the detail on a mill but unless your supplier has both machines it's probably easier to Make just the one file to cnc mill the lot from scratch.

Talk to the shop about what flavour file they can use. It can take a bit of tinkering to figure the translations. IGES143 is usually a good start.

[Donor]

If you can authoritively tell me what sort of tolerances I should be allowing for parts (non-moving parts) so that they fit together nicely without jamming or being too loose then that would earn some bling

Well, you see... I was about to do just that, when I realised that others have pretty much got that covered.

...or at least will have it covered soon.

So uh... yeah... *cough*

[Mental Trousers]

What are you using to make the pictures?

Rhino 4

The slotted hole at the base of the brake cyl mount looks wrong. Makes for a comparitively weak area at the bottom of the brake mount arm, I'd add some material to the sides to bulk up the cross sectional area.

The rear brake is only there to satisfy the rule book because I never use it. I'd pull it off and save weight but I'm not allowed to. So I'm not to worried about the cylinder mount. I made it a slot because it never quite lines up the bottom mount with either of the 2 sets I've got and requires a fair bit of dicking around.

I'd also radius the external corners and fillet the internal ones by p'raps 2mm, less stress raisers all round.

Fasteners that size are typically 2 - 3% undersize, so if the fastener is also doing duty as a locator then 0.1 oversize is good.

Mint. Cheers

[Grumph]

Don't forget you must have an up - stop for the pedal too...make it adjustable. I usually do a comma shaped stop with a 6mm c'sunk screw retaining - swing it round as an adjustment.

I always laugh when someone says they don't use the back brake...a mate in the early days of F3 said just that and put on an auminium disc...
Went to a steel one after 3 meetings as the alloy one was worn out...
His conscious mind said one thing but the unconscious did quite another.

[Mental Trousers]

Don't forget you must have an up - stop for the pedal too...make it adjustable. I usually do a comma shaped stop with a 6mm c'sunk screw retaining - swing it round as an adjustment.

I always laugh when someone says they don't use the back brake...a mate in the early days of F3 said just that and put on an auminium disc...
Went to a steel one after 3 meetings as the alloy one was worn out...
His conscious mind said one thing but the unconscious did quite another.

Usually I ride the bike without any fluid in the rear brake because I literally do not use it. But for race days and track days that do scrutineering I have to have a working rear brake.

If I could I'd move the gear changing to the handle bars so my feet don't have to do anything except give me a steady platform to ride from. But I don't actually fancy that idea, too many things to do with the hands. Simpler is better and having 1 job to do per hand suits me.

[Ocean1]

Rhino 4

Figured, I use it a fair bit.

Been using it long?

[Mental Trousers]

Less than a week.

[Ocean1]

Good tool for typical Kiwi industry, quite intuitive and flexible. You'll get the odd failure in boolean operations and fillets but even the top end Mcad app's do that and they're way more restrictive to use. And about 10 times the price.

[Sensei]

Use either 2017 / 2024 or 7075 grade Alloy as these are the only grades that would be suitable for making this type of components out of .

-T351 Solution heat treated, stress-relieved stretched, then cold worked

T651 Solution heat treated, stress-relieved stretched, then artificially aged (precipitation heat treatment , 2014 alloy combines excellent machinability and high strength with the result that it is one of the most widely used alloys for automatic screw machine work. It is a tough, ductile alloy suitable for heavy-duty structural parts.

Chemical Composition Limits

Si = 0.50to 0.90
Fe = 0.50max
Cu = 3.9-5.0
Cr = 0.10max
Mg = 0.2-0.8
Ni = 0.1max
Zn = 0.25max
Ti+Zr = 0.20max
Shear strength: O (annealed) temper 18 ksi, T4 temper 38 ksi, T6 temper 42 ksi
Machinability is somewhat more difficult in the heat treated conditions. For lathe cutting use 15 degree top rake, 20 degree side rake and 10 degree clearance. Use of a lubricant, such as oil or kerosene, is recommended for all machining