Drawing Assistance Needed.

[pomwah]

I'm investigating the possibility of having some custom disc brake rotors made in the PRC.

 

What I'd like to do is provide a "proper" drawing of the rotor that can be followed by a manufacturer. My problem, and why I need help, is that I haven't the foggiest idea of how to set the drawing out or label the key features.

 

This is what I have so far,  any pointers?

 

[GT6MK3]

needs more detail on the 6/12.5mm extra pockets.  which is it, on which side, to which depth?

[esxefi]

yes, include them and the other 4 holes as hidden detail, like you have done with dotted lines to indicate material thickness on the lower plan elevation drawing.

[JohnD]

 

Hope this big enough.

 

You appear to have drawn a recess in the edge of the inner hole - but no dimension to its depth.

 

Do I misinterpret?

 

And I'd add the AA line to indicate the lower drawing was a section.  If those holes with two diameters have are counter bored, then the section could make it clear.

 

John

Edited October 25, 2014 by JohnD

[pomwah]

Thank you gents.

[pomwah]

Modified drawing:

 

The MGF standard centre hole is not recessed, to make it a little easier to machine I removed the recess shown in the first drawing.

 

This is basically a Mazda MX5 NA 231mm rear disc with MGF drilling.

 

Edited October 26, 2014 by pomwah

[JohnD]

But John,

The countersunk (AH! Countersunk) holes are on the PCD radius of 95.25mm, not the centre hole radius of 66mm, so in the section they should be shown there not overlying the edge of the hole.

Or are they?  No indication on the drawing of their radius from the centre.

Oh, and no spec. for the thickness of the top hat wall

 

Sorry to nit-pik, but the point of an engineering drawing is that it is correct AND avoids all possible confusions.  I try to imagine how I would make the part, and where I'd have to go back to the customer for more instructions - which neither of us want.

John

 

PS and if you want me to really, really pick nits, and make it look a proper job then Title Block, saying what the part is, who you are, date, material, finish,scale.  You don't need spaces for checker, signed off, etc. but include your address, phone.

Edited October 26, 2014 by JohnD

[pomwah]

All good John, thanks. I drew the countersunk holes in the side view like that because I thought it was supposed to indicate what the top view would look like if sliced through the middle? I would have added the stud holes but it would be more messy than it already is.

 

The plan is to make the drawing "foolproof" so any Chinese machine shop could follow it and produce what I want first time.

 

Nit pick away!

 

Cheers. J.

[pomwah]

With regard to the "Title Block" are there any metallurgists, or just plain knowledgeable folk, out there that can tell me what an "everyday garden variety" disc brake rotor should be made out of?

[Triumph-V8]

They are from cast iron

if better quality is needed they are GGG

a special quality with ball form carbon inside not sheet form.

 

Sometimes the cast iron is improved by adding chrom and Nickel.

If you put that on the lathe it makes not that black dust but is a bit similar to steel.

 

Sometimes they get a heat treatment that hey do not bend when used

 

Anyway normally I pick a rotor from another car if I want to improve my brake

and make them fit on a lathe and drill new holes.

So I take the material the car company had choosen.

[pomwah]

Vielen Dank.

[JohnD]

John,

Yes, even drawings are potentially confusing.  That's why engineering drawing uses a number of conventions, to help make them clear.   One is called "orthographic projection", which imagines that the solid part is in a box, and its dimensions are "projected" onto the 2D sides of the box, including holes and other details that could not be seen from that box side.   The ways of doing this are further conventionalised into "First projection", a European standard, and Third Projection in the US.  The UK usually uses 3rd Proj.   See: http://en.wikipedia.org/wiki/Multiview_orthographic_projection

 

A crude way of discriminating which is which is the layout of the various views.   Third Projection shows the Plan view above the Front view, with the Side on either side of the Front.  First  puts Plan below Front and Side.   However, a circular structure lacks Front and Side views that are different, so no side is shown. 

 

This is what you drew, but your bolt and countersunk holes should appear in the side view in the same relationship to the rest of the part.  If the holes will then overlap confusingly, "section" lines across the plan view that intersect the holes can make them clear, as they are only shown on the side view that that relates to a particular section line.

 

John

[egret]

One of the early lessons I learned in my first proper job" is that a fully defined perfectly drawn engineering drawing is useless if the guy making it doesn't understand it.

 

I'm all for correct engineering drawings, but my experience is that you need to tailor the drawing to the person who will be reading it.  If you are shipping this work out to PRC then this may not be possible.

 

My quick disclaimer is that my experience is with fabricators not machine shops and I have no experience with dealing with the PRC, but hearsay is that several layers of idiotproofing and checking is required to ensure you end up with what you want.

[pomwah]

Thanks guys, I'm taking your comments on board and starting a new "improved" drawing. Hopefully I'll get enough information into it to make it idiot proof. More as I get closer.

[motov8id]

this is from the Brembo Cat.http://bremboaftermarket.com/En/Car_Disc_Catalogue/Catalogue_Detail_Image.aspx?Code=12d2da24-e34f-4659-96b0-eb18f4e591d0

 

 

Edited October 28, 2014 by motov8id

[JohnD]

(Squawky voice)   "That's the way to do it, heh, heh, heh!"

[pomwah]

The latest and with luck, the last, version of the rotor diagram. No "Title Block", sorry John and somewhat different from the Brembo diagram, thanks MotoV8. I think I've included everything that needs to be there.

 

Scale approx 1:1.

 

Pick away!

 

[motov8id]

You left out the chamfer at the bottom of the center hole probable necessary to get the rotor to sit flat.

[2.5piman]

Hello Pomwah,

 

I would suggest a 3mm radius on the internal corners, sharp corners make cracks more likely to develope? Are you planning to have these cast or machined from solid, as if the former, the vertical section should have about a 3 degree taper so as to allow the pattern to release from the mold, parallel forms just won't release.

 

Alec

[pomwah]

You left out the chamfer at the bottom of the center hole probable necessary to get the rotor to sit flat.

 

Cheers, I'd considered adding a chamfer, as in the first attempt, but the MGF rotor hasn't got one so I elected to specify the larger 66 mm straight sided centre hole.

 

Hello Pomwah,

 

I would suggest a 3mm radius on the internal corners, sharp corners make cracks more likely to develope? Are you planning to have these cast or machined from solid, as if the former, the vertical section should have about a 3 degree taper so as to allow the pattern to release from the mold, parallel forms just won't release.

 

Alec

 

Thanks, putting a radius on the internal corners is something I would never have considered. Given the cost of labour in the PRC I'll leave it up to the supplier to decide how they want to make them but I'd imagine that machining them out of a billet may be the most cost effective option for a small run of 10 rotors.

[pomwah]

Quick update.

 

I sent the drawing to three Chinese engineering firms specialising in brake rotors and prepared to do small runs.

 

Prices range between US$20 to almost US$40 per rotor and shipping ranges from US$25 to US$30 per rotor delivered to my door. Approximately 10 days to produce and 4-7 days to get to me.

 

The MX5 hub flange does not differ significantly from the MGF unit, I'll be getting a collar shrunk onto MGF hubs and machined down to fit the MX5 bearing and thus the upright.

 

Progress!

Edited November 11, 2014 by pomwah

[GT6MK3]

Do you still have the contacts for these?

[pomwah]

I do.

 

I have spare discs if you want a look at one, if you wanted the same dimensions Wex will have the casting buck.

 

Grace Yuan
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Edited October 23, 2015 by pomwah