foregive me if this is a silly question, as i don't have extensive knowledge on the topic, but why is no one doing this? or is there a company doing it? doesn't seem that it would be a difficult part to produce. just curious

 

It can be done, and it has, the parts thats difficult is getting the chrome insert correct and pressed in. If you look up the 12 rotor boat build, thats how he built his housings.

The other problem is cost, its EXPENSIVE, and you would have to sell thousands of them to make up your cost to produce

 

Because it'd be expensive as hell aimed a minuscule market.

 

See this thread. Reasons are scattered though out.
https://www.rx7club.com/2nd-generati...s-car-1074418/

If you have lots of money Racing Beat makes front, center, and rear out of Aluminum.
Engine Rotor Housings & Aluminum Side Housings - 1986-92 Mazda RX-7 Performance Parts

 

It would not be that hard to machine for someone with the resources. I believe the steel liner could be eliminated for a cermet, flame sprayed coating, hard anodized (maybe first before other coatings), and other now available coatings. I've seen aluminum with coatings that a file couldn't cut (files are pretty damn hard). How long would it last? I dunno...

And then there is the oil retention capabilities that have to be figured in.

 

Porsche moved to aluminum cylinders from cast iron (with a short and unfortunate interlude with cast iron sleeves with aluminum fins) in the early 70s because they shed heat better (critical for air cooled engines). In order to handle the abuse, they treated them with Nikasil. It has good thermal, wear, and oil retention properties. If it can handle the heat of an air cooled engine, the heat issues with a rotary should be no problem. I imagine the issues with ring/apex seal wear would be similarly well handled. The only potential issue I can think of would be oil retention, but if the chromed steel can handle it, I imagine the Nikasil would be just fine. In addition to likely being functional, I would be willing to bet dollars it's cheaper than having the chromed steel insert made. LN Engineering makes Nikasil lined aluminum cylinders for Porsche and VW applications, and I imagine they could probably handle a rotor housing at a reasonable (comparatively) cost.

 

That would sure seem the way to go.

To the original question the OP asked, as long as a good 3D digital model of the housing was available, machining the thing out of a good chunk of aluminum tooling plate like 7071 would be easy peazy for someone with a CNC machine large enough to do it. To pay a shop to do it based on their shop rate may not be that cost effective. It would be best to be able to use the resource (work there and talk the boss into letting you do it basically free, I get to do that) or own it.

 

yea i work for a diesel shop and we may be starting a relationship with a company that remanufactures engines on a pretty large scale. the manager came down to see us this week and brought with him a duramax head that his company CNC'd to show us the improvements they'd made to it. that's when i got to thinking, maybe they could do this with housings. making improvements and such. i realize the equipment is costly. their company has over 10M$ invested in equipment and tooling. but i figured the cost to manufacture, if you've already got it, isn't so extreme and profits could be seen. i wouldn't bring this up yet, of course. but maybe further down the road

 

This is the key. We have a scanning CMM and I've had some simple things done. A complete rotor housing? I don't think the boss is going to go for that. If you have (and know how to use the software) or know someone that has Solidworks, it may be best to just create a reasonable digital facsimile of the original. A lot of what was done like draft in the coolant passages is really unnecessary. It's just to remove it from the mold. Some other things like recesses around the exterior could be ignored also.

I think this is the first time I have ever quoted myself. Lol!

 

my brother (the owner of the shop) has a 3d printer, and solidworks. i talked to him a bit yesterday about it. but as mentioned, i don't think there's really enough of a market to make it profitable right now. not sure if there ever will be

 

A good comparison is Racing beat's aluminum iron prices. They are about 3x the price of a new OEM piece ($1500+ per piece). They aren't that greedy, it is just expensive to make compared to the OEM piece.
If one of the guys with connections at a machine shop could price an A356 (racing beat uses it for their irons) aluminum billet for this, that would be interesting.

Of course one day it will all be NLA and the used parts market will dry up. So this may be the only option for replacement parts.

 

No, there isn't and no, there won't.

Jay Leno could do it- easily- but how many others have access to the technology, the expertise to utilize said tech and the money to finance the upfront costs (no one has even mentioned the cost of all the aluminum billets it starts with...)?

Other than the Lenos of the world (all couple hundred of 'em) the only other potential market for such a big ticket item would be racing and racing requires sponsors and what sponsor is hot to sink money into a dead end tech motor? I doubt even Mazda would show much interest.

 

The problem is not technology, It's making money making them. CNC machines are very common nowadays. I have a friend with a small garage shop that has two Hurco VM1's each of which could easily machine the part (ones for sale, $22,500). Making the model requires some expensive software that even small shops have. My friend does not have modeling software, but many contract designers own their own seat.

And yes, clokker, the chunk of aluminum would be quite expensive. This is exactly why a large company that plans on mass producing something out of aluminum turns to other means like die-casting or molding. The mold is very expensive but will produce hundreds of thousands of parts that need minimal machining to be ready to use. The end result being cheaper than machining the part from a billet. RB cast their aluminum side plates instead of machining them because the part really can't be machined without very significant design changes to the oil return and coolant channels. Not saying it couldn't be done but...

 

i just found out you can 3D print in chocolate, and we have an OK CAD model of a rotor housing, so who wants a chocolate rotary? i bet with the right coating, like an M&M it would be able to withstand being in the car on a sunny day...

 

a sunny day where?

also lets go the extra mile and make the middle housing and two rotor housings on solid piece assembly would be a little extra awkward assembly but think of the strength it would add, at the sacrifice of interchangeability. this is what i want to 3d print in alum and then press in chromed steel inserts like big yellow cats (mr smith). when the housing surface is no good, pull the incerts out and press in new ones. and good for another round... when i have $200k to get it done right.

 

$200k?

i think there are two reasons to go to CNC rotor housings. the first is cost, new from Mazda, at a non muggle price, a rotor housing is like $650. it would be nice to have something cheaper, it wasn't that long ago that Mazda sold rotor housings for like $350...

the second is the ability to move the port(s) around. or add a 3rd spark plug, and maybe another metering nozzle. or do 10A/12A or even 13A or 16X housings

from a design point of view the sheet metal insert is nice, but the MFR housings didn't have it. you'd obviously loose durability, but if its cheaper to make in the first place.....

it is also a bit weird nobody has tried nikasil or some of the new coatings on a rotary, i don't see why they wouldn't work?

EDIT: not sure why i quoted you Mr Phase, my response isn't even relevant to yours

 

i'm thinking 200k is a fair start up to get the ball rolling, with more needed after a working product is demonstrated. how much does an aluminum 3d printer cost after all? one accurate enough to do as i describe?

it could be cast and then CNC'd down to spec for cheaper that's for sure. and maybe the new coating technology is the way to do... i'd guinea pig it for sure. lets casts some rotor housings in alum and then come back to 3d printing them...

 

The Nikasil seems like a good replacement for the steel liner. Why mess with a liner? If you catch the coating going bad, re coat. It's fairly thick and can be redone.

 

3d printing would get you one fairly expensive part that still needs finish machinig. If you invested a very small amount in sand casting the piece you envision, you could do it over and over again in far way less time and money than printing just one. Would a sand cast be strong enough? What about residual sand in the casting? You need to do some more research. The companies making the stuff they do today use the processes they do for a reason.

 

that factory housings are cast... and we have a thread about casting that j9fd3s has showed great info, i'm looking into casting at the moment.
3d print a housing in plastic, and use that as a base to make the sand mold, then fire the mold to make it hard/ melt out the plastic, and then fill the cavity with alum. bam! rotor housing.

which brings up another question, what about getting molds from mazda japan??? wheres our jap friend on this one..
if done right, completely avoidable.

 

The housings appear to be die cast or permanent mold (mold is steel). there is always some sand in the part when using a green sand mold like in the video in the other thread. Higher quality parts are made using sand molds that have been fired to make them hard. Just like the core the guy uses in the same video. I suspect this method is used for the rotors.

 

https://m.facebook.com/pages/Billet-Inc/489059381142420

 

there is a video on the mazda website of them making rotor housings. maybe you could review it and tell us if the sand is fired? I can't tell either way... but its' definitely sand.

 

I haven't priced aluminum lately, but from the most recent prices I recall when doing machine work a block of HIGH QUALITY aluminum of the size to make a rotor housing would run ~$200-$400 each in just materials.

Factor in the price of the CNC machine and it's just not possible to CNC them for less than Mazda sells them.

The only real hope for an economical production is a cast iron unit with chrome coatings made in large quantities in China. No, it won't be as reliable as Mazda's castings, but we're talking economy models here.

 

China already makes iron rotor housings. turns out that iron is unusable as a rotor housing material.