As I have mentioned before, you need a very experienced machinist with all the correct tools to make this component accurately. We did not grind the shaft, it was only turned. Since it was made correctly I did not need a bearing only a PEEK support.
Initial build of Twincharger
- Thread starter matnrach
- Start date
It was bored but the sizing was better than 3 microns but the concentricity of the bore to the rest of the shaft is critical
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WB projects
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I am a experienced machiniste and just for fun, put you motor in the chuck and put an indicator on your shaft where the impeller goes. Dont turn the chuck, but turn your shaft by hand instead. The best I had is 0.002" of offcentric
19:30 in the video
19:30 in the video
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It is in the car at the moment but I will do. Anyhow at full speed there appears to be no vibration and the peek centre support does not appear to touch. We will see at 100000rpm with the new TP motor!
have you measured the run out of the motor shaft on its own? - clamp the motor body on a Vee block and rotate the shaft, dont use a lathe
WB projects
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Like you see in the video, on a Vblock or on the lathe there’s no differences. The run out is 0. If I had turn the chuck instead of the motor shaft when it was mount in the chuck, it would have been different.
GTHound
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I love the pictures, they have been helpful as I am modeling out my design. Thank you
GTHound
Active member
It’s good to see you back WB! Thank you for the update and including some video footage of your build. It has been helpful for me to think through my design!
I am just a hobby machinist but I know that a concentric hole cannot be bored with a 3 jaw chuck. Even with a 4 jaw, it would be difficult to center the work to get accuracy in 0.0001" vicinity. I recently acquired a vintage Mikron T90 lathe. This is a high precision Swiss lathe. The work holding is with collets. I don't have the lathe powered up yet (installing VFD) and haven't checked the run out on the collets. But I have hopes for it. Alternately I have a friend with a Hardinge tool room lathe that uses 5C collets. Hardinge has special accuracy collets with a TIR of 0.0002". So I have hope that I can make an extension shaft with very little run out. Maybe I'll fail but I'll have fun trying. I'll try to make the extension shaft before buying a compressor.
WB projects
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there’s so much way and tricks to make it concentric and it is really hard! Can’t wait to see your work!
To obtain the correct bore it is best to get it within 10-15 microns undersize and hone it with a honing bar made from PEEK and then use diamond lapping paste.
Interesting thought on honing. I'm also thinking about trying an adjustable reamer. I ordered a short 3/8" shank 1/4" HSS boring bar today and a piece of 3/4" 12L14 cold drawn round bar. Let the games begin!
To be honest the build of the supercharger was simple compared to the infrastructure required to run it properly. At least it was for me.
GTHound
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I hope that works out. I have a boring bar, but don’t think that I could work with that type of precision. I am going to explore another route. I have my 3D CAD design complete and am going to have the extension shaft done in laser sintered stainless steel. I did this once before for a valve shaft and was quite surprised and pleased with the results. The cost to print it at shape ways is $43. Also, I don’t anticipate that the requirements are as stringent when working with a shaft that has a flat on it.
Maybe but I really didn't want to experiment and made it the absolute best it could be.
GTHound
Active member
The 3D printing is a pretty cool approach to get the design right and right up my alley as I already have this capability. It opened up the possibility for me to get started with my design and build without the big commitment and cost to get metal parts made. I have gone through multiple iterations trying to get the spacing right between various components and approaches to connect and support the motor to the compressor and backplate.
I chose to print with my standard ABS filament, which is pretty stiff and better temperature resistance than some other filaments. Although my most recent filament (hatchbox) doesn’t behave like ABS. Did you print it solid or what percent infill density? I was printing at 20-30% infill. But, I am going to reprint with cubic infill pattern for strentgh (I was printing zigzag) at 75% infill and slow it down to 70 mm/sec for better layer adhesion.
Also, I just looked up what a compressor limiter was as I had not heard of them before. That totally makes sense! I like the idea of having a metal sleeve in the plastic hole for the screws to press against.
I tried machining some various approaches in my home shop this last week while waiting for the laser sintered stainless shaft to come it. I have found what you said to be true. What I thought was a straight hole is not straight enough. And what I thought was concentric, is not concentric enough. And I have struggled with tolerances. It is a combination of limited equipment, and limited experience. I went through a handful of various couplings trying to modify them with a boring bar. My most successful experiment this week regarding the shaft adaptor was 3D printing a little adaptor sleeve to go around the stock cut off compressor shaft and then press fit it into a 10mm x 8 mm aluminum couple to connect it to the 8 mm motor shaft. I thought about going down the path of getting a lathe, but that is too much expense, too much space, and of course, I don't have the skills.
One issue I am having is that I have no interference between the compressor wheel and housing upon assembly, every thing rotates freely. But as I adda little RPM, I start hearing the ringing of the metal touching. I seem to have similar clearance similar to that of the original turbo charger design. But, I really have not figured out a good way to measure the clearance. One hypothesis is that the compressor wheel is starting to generate compressive force and is starting to lift off like a helicopter. I just tried to flex the backplate with a lot of force, and I can see a little deflection. Maybe I will try to measure it. Another possibility is that somehow my motor mounting is slightly off axis. I will check that next. Perhaps it is time to upgrade to an aluminum backplate or maybe try the carbon fiber filament for 3D printing if my above plan doesn't help.
Maybe the shaft extension or the motor shaft itself moving or flexing. Maybe my cheap bearing has too much play and flex. Maybe all of this will go away when I get a one piece shaft extension. Although, there could still be alignment challenges. I think I remember WB saying he had a similar issue with the compressor wheel contacting the volute housing. Have any of you encountered issues with axial movement?
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GTHound
Active member
I love the video. Thanks for capturing the build. I have watched it several times. And it has been helpful to me.
I don't have any contact with the compressor wheel and the housing (so far). I made the position of the wheel relative to the housing exactly the same as the original turbocharger. The PEEK front support (not a bearing) seems to be fine as is the carbon nylon backplate. As I have mentioned it is absolutely imperative that the shaft is made extremely accurately. Is there any end float in your motor rotor?
GTHound
Active member
Good question. There seems to be very little end float. I think it is mostly a combination of the nut loosening due to fast deceleration and flex in the back plate. I am still waiting on my laser sintered stainless shaft and hopefully they works for me. Here is the update. I will start a build page for my project as it is looking promising.
Well, my goal this weekend was to make some sort of boost in the basement And….At the last minute, goal achieved!
I was basically struggling to overcome the instability of 3D printed parts flexing under load and the compressor nut loosening causing interference between the compressor and volute housing.I greatly increased the rigidity of the backplate by probably 5-10X. I started using a cubic infill (vs zig zag) at 70% (up from 20% infill) and slowed down my printer to 70 mm/sec to get better layer to layer adhesion with my ABS filament. Once the design stops changing, I will eventually make an aluminum back plate. Problem solved.
Then I got out the dial caliper and made some adjustments to get the extension shaft run out below about 5 thousandths of an inch. This is the best I can do with the coupler approach as an interim solution as I wait for my laser sintered stainless extension shaft.
One problem that I had was the electronic brake. The compressor wheel was slowing down too fast and the nut would come loose and the compressor wheel would lift off and touch the volute housing. I am tuning the brake settings and letting it coast a bit more and ordered a 10 mm x 12 point socket so that o can tighten the left hand thread nut in place without taking apart the assembly each time. I had initially applied the brake settings as a safety mechanism, but turns out that it might just make things more dangerous. For the final assembly I will probably use loctite, but right now it gets tore down and put back together several times a day.
Earlier in the week, I had only spun it up to about 0.1 PSI before things would get wonky. I didn’t even think the amp meter was working on the Electronic Speed Control data logger.
But with a more concentric and stable set up, I then spun it up to about 0.4 PSI, the 1 PSI today and was rejoicing. Then got bolder and wound it up to 1.5 PSI. Then I went for 2 PSI. I can’t remember where I finished but it was north of 2 PSI. I don’t know if I will get much beyond this without the new shaft which hopefully gets runout of less than 1-2 thousandths.
Below is the data log from the last pull of the day. At the 3rd peak is where we hit somewhere in the order of 2.2-2.4 PSI. I was so excited to be able to make boost! From here it is a matter of refinement, continuous improvementand optimization.
Here are some key observations I make when looking at this data.
- Lots of Data: I love having the data handy so that I can see what is going on and tune the system. That said the downside is that I am missing some data, like motor temperature and PSI as they are on different measuring devices. I was for instance happy to see that the ESC accurately tracked voltage and amps real time, so I could put my multimeter and amp probe away and focus my eyes elsewhere.
- Right Voltage: I decided to go with a higher voltage battery than the motor says it can handle. This is what I think WB said he was doing and confirmed by Castle. I built a 12 LiFePO4 cell x 3.25 volt battery = 39 volts nominal. This is where the purple line starts. But under load you can see it drops to 33 volts. Interestingly, the Castle 1721 says it can handle a maximum of 33.6 volts. I still need to get a proper charger as I am charger half the bank at a time.
- Digital RPM. I simply changed the setting in the app on my iPhone and configured the ESC for 4 pole motor. The digital readout on APP is then actual RPMs of the compressor wheel, since it is direct drive. The highest the RPM for was about 45,000. This motor is rated to 90,000 (which is where the rotor flies apart). I need to put a safeguard in to stay well below that number with a safety margin. That said, more RPMs = more boost!
- Amps: I thought that my ESC was not working right, but it turns out that it can’t really measure anything when idling along at just a few thousand RPMs. I was slowly getting more aggressive. On this last run at over 2 PSI, I hit over 71 amps (red line). Throttle (blue line) was at 39% and RPMs were an out 45,000. So, there is still some headroom and hope to get to the targeted 5-7 PSI boost.
- Heat. I have heard of lots of ESCs (electronic speed controller) blowing up and catching fire. So I spent extra money here and bought the biggest one I could afford (high end of the low end). It is a if chunk of meter with a lot of built in cooling and no surprise. It runs cool. It did not quite get up to body temperature. The motor. That was a different story. It got hot.
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