My first wankel engine 'bits'!

[itsme]

Hi there,

Well, I finally got my mill working in 2 axes and after a day of drawing pretty pictures with a pencil in the chuck, I decided that I would try some proper machining. Seeing that my z-axis isn't ready yet, I was pretty much restricted to 2D profiles only. The obvious choice then, was to have a go at some wankel parts in aluminium.

I made a small housing as well as the rotor to fit it. I used my Excel spreadsheet to generate the Gcode for the housing and CAD/CAM to do the rotor. I have now modified my spreadsheet to take into account the tool radius when it generates the Gcode, so machining is easy. It can also generate code for a housing that is parallel to a true epitrochoid, which is what a running wankel needs. I needed to include the radius compensation, as I am using TurboCNC which can't do this on its own.

The big test to see if my spreadsheet actually works was whether or not the rotor would fit properly inside the housing. I kind of shocked myself a bit with the results. It is spot-on!

This particular 'engine' has an eccentricity of 2.86mm, a rotor radius of 20mm and the epitrochoid is 0.4mm larger all round than a true epitrochoid. The capacity is 4.12cc and it was cut using a 6mm endmill.

I'm now one step closer to building a running engine! Once the rotor and housing can be made (which they can now), the rest of the engine is relatively simple to do.

I've included photos of the rotor and housing as well as my mill.

Regards
Warren

[ViperTX]

Cool...any plans....what are you using for rotor tip seals?

[itsme]

Hi there,

If you mean engine plans - no. I'll pretty much design the whole thing.

I'm still looking at the metallurgy side of things. There are a few combinations of apex seal and housing material that minimise wear and chatter marks. Unfortunately, a lot of these processes are not really available to Jimmy-Pop in his home workshop...a lot of them involve 'fancy' plating processes and things like carbon seals. I'm thinking about maybe making the housing out of steel and having it hard chrome plated and then making the apex seals out of cast iron (something like piston ring material). Luckily, small engines like this don't tend to be used very much so the metallurgy is not as critical as it is in some applications (like cars).

The only other part that I'm a bit weary of, is the internal gear that's used to phase the rotor. I've never made any gears, yet alone an internal gear. Sadly, no one seems to make these things in the right sizes, so off-the-shelf parts are out. That's the next big challenge!!!

Regards
Warren

[mxtras]

Nice work!

BUT - the mill and surrounding area is entirely TOO clean....'you milling, or cleaning? Get back to milling!!



Keep us up to date! Hopefully you can get a mini Wankel running! I am sure that would be a first.

Scott

[itsme]

Hi Scott,

If you look at the photo, you'll see that the chuck still has a pencil in it. The photo was taken before any metal was cut - it won't always be that clean, honest...

My plan is to have an engine working in the next 3 months (since I've got nothing else to do for the next 3 months...). I'm fairly sure (know) it can (and will) be done. It won't be the first though. I've got a 5cc OS Engines wankel, which runs pretty damn well. There have also been a few others that people have made, but not many at all. I've only ever heard of 2 others.

Regards
Warren

[RotarySMP]

The SW92 wankel form VTH.DE is made completely out of medium carbon steel, with the rotor and housing chromed. Don't loose too much sleep over the materials. The really critical thing will be getting the rotor to side housing clearances tight enough for a good gas seal.

[pleasuretool]

yeah, i agree. with the small pressures involved, and affordabilty of such a small rotor... i don't think apex seals are terribly important, even if the tips of the rotor wear out over time, pop a new one in. I'm still trying to get my mill going, and i plan on doing a lot of IC projects. so i'm watching your project with great interest.

[MIKE JEFFERS]

itsme
these home built cnc's are cool as **** ain't they
but what about your z axis , it's the least hassle to build.
mike

[itsme]

Hi Mike,

I think that this CNC mill is the coolest thing I've ever had. After the first time I used it, I couldn't believe how relaxing machining could be and how clean my hands were at the end!!! It's great!!!

I guess the z-axis could be looked at as the easiest axis to convert, but I decided to do things differently. I thought the standard leadscrew looked a bit 'flimsy', and I don't think it was ever designed to be used for accurate positioning, as in CNC machines (although MANY people have used it successfully with CNC). For this reason, I have decided to scrap the standard leadscrew and replace it with a 12 x 3mm trapezoidal screw. The reason that it is taking me longer to do, is that I have machined a new aluminium bearing block to take angular contact bearings and I also have to replace that entire arm that connects the leadscrew to the head (yes, that big steel lump...). I'm hoping to have the lump rough machined where my dad works, but sadly, it's not their first priority, so I have to wait. I'm also going to use a counter-weight on the head.

Once the z-axis is done though, I'm pretty sure I'll be making some awesome engine parts. I also have a few new ideas for a rotary engine, but I'm just trying to get them down on paper to see exactly what they all involve. I think a bit of 'design time' is in order - then the fun can begin!

I love CNC!!!

Regards
Warren

[DAB_Design]

Originally Posted by itsme and how clean my hands were at the end!!!

Ok, I must be doing somethign wrong!

[CJL5585]

Itsme:
I used my Excel spreadsheet to generate the Gcode for the housing and CAD/CAM to do the rotor.
--------------------------------

Love your wankel project. You are looking good. I am interested in using Excel to generate the g-code. Would you, if you have time, give me some more information on the Excel process.

Appreciate it.
Jerry

[RotarySMP]

Hi itsme,

I disagree on the apex seals. You will need them. There is no way you are going to get a metal to metal sliding fit on the three rotor apexs all around the trochoid. One leaky apex is two chambers without compression. You will never get it started.

It is the side seals you can do without on a small motor, as you have a large surface area slowing the leak rate, but even then you need to control the clearance very carefully. There is a good article on the web of a guy who had to lap the rotor housings of his OS/ Graupner, which should give you a good target for this clearance. Couldn't find that article just now, sorry.

The SW92 has simple one peice apex seals with a simple U shaped spring preloading them. I think they are also just hardened steel.