Author Topic: Halfa, a DOHC inline Twin  (Read 21966 times)

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #45 on: December 05, 2022, 04:16:09 PM »
Thank you, Brendon.

Thanks, Dave. I considered ball bearings, but I'm currently planning on plain bearings, either 660 bronze with splash lube, or Oilite and maybe an open crankcase. The latter scheme worked out well on the v-twin, and I do like seeing into the "works". I don't imagine asking this engine to rev to 8000 rpm as I did at least once with my old Alfa. If I'd opted to do the full on 4 cylinder version my thinking might be different.

Thanks, vtsteam. Yes, I wrote center height, then proceeded to use the value for swing-over-bed.  :facepalm: The correct center height is 1/2 that, or 2.25 in. I've corrected the table. I appreciate you waking me up...
Regards,
Ron

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6138
  • Switzerland
Re: Halfa, a DOHC inline Twin
« Reply #46 on: December 05, 2022, 05:35:34 PM »
Coming along rapidly  :praise2:  :praise2: :wine1:

I've had my 12cc twin over 8 000 rpm however that has ball bearings for main bearings.
Best regards

Roger

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #47 on: December 08, 2022, 01:02:41 AM »
Quote
I've had my 12cc twin over 8 000 rpm however that has ball bearings for main bearings.
Hi Roger. I haven't ruled out ball bearings yet. See my scheme below for decision postponement.

I'm next turning my attention to the crankshaft. I'm planning to get it out of solid bar this time, so I ordered a piece of 1144 “stress proof” steel to maximize my odds of success.

In the first picture you can also see that I've made and installed a couple of bronze main bearings. Flanged Oilite bearings for the same shaft size have a slightly larger housing OD, and ball bearings have are even larger still. This means that either of those options are still available to me just by increasing the bore in the crankcase. I also received the o-rings that will seal the cylinder liners in the block. You can just see one of the upper ones in place.


I didn't take any pictures of the preliminaries, but the the bar was centered in the 4-jaw on the lathe with the outboard end in the steady-rest. This bar was so nice and smooth as received that I didn't even have to turn a spot for the steady to ride on. Haven't had one so good before! With one end center drilled I turned it around and did the other. Then I went to the mill and cut shallow flats lengthwise on either side. These gave me a two parallel surfaces so I could then stand it up in the vise and drill for the offset centers at either end. Back on the lathe I turned most of the OD to the major diameter of the crank webs, leaving a short length at one end still with the flats for registration later. Shifting it to the offset centers, I stepped off and marked with a plunge tool the locations and widths of the conrod gaps under the crankpins. You can see these marks in the next photo.


Then I began to mill away much of that waste material. This is about as far as I got by quittin' time today.
Regards,
Ron

Offline vtsteam

  • Full Member
  • ****
  • Posts: 753
Re: Halfa, a DOHC inline Twin
« Reply #48 on: December 08, 2022, 01:38:51 AM »
For a second I thought that was actually a stick of carbon! Duh... I was wondering what it was for? Not quite so crazy as it sounds bc I have a stick of graphite about the same size, for hot air engine pistons....but I knew this was IC! Carbon steel, of course. :facepalm:

Ron, how do you know what size to make the counterbalance weights in advance?

Great seeing you carve that out!  :ThumbsUp:  :popcorn:
« Last Edit: December 08, 2022, 01:47:17 AM by vtsteam »
Steve

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #49 on: December 08, 2022, 03:31:40 AM »
Thanks vtsteam.
Quote
how do you know what size to make the counterbalance weights in advance?
I do my design work in Alibre Atom3D. One nice utility it has that I'm trying out here is it will calculate a center of mass for you. I told it that the crank is carbon steel, the rods and pistons are 6061 aluminum, and it does the rest. I haven't included the piston pin, the rod bearings, or the cap screws at this point. As you can see, the CG is just a bit above the crank centerline as it sits now. Of course, I don't know exactly what their algorithm looks like, so I take it with a grain of salt until it's confirmed in the flesh. I've drawn it with about as much counterbalance as I'm willing to. Hard to add much more, but I can easily remove some or a lot.
Regards,
Ron

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6138
  • Switzerland
Re: Halfa, a DOHC inline Twin
« Reply #50 on: December 08, 2022, 08:55:25 AM »
Balance calculations for a 360° crankshaft are interesting. There are various ideas on how much of the piston and conrod weight should be included, 50% is often suggested. When I was designing my 360° crank Alex S kindly made some balance calculations in 3D CAD. This is what we ended up with:

The machining of the crankshaft is here, however I expect you have already looked at it.

https://www.modelenginemaker.com/index.php/topic,7883.240.html
Best regards

Roger

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #51 on: December 08, 2022, 02:44:45 PM »
Thanks for that, Roger. While I've been following along with your build threads, I've only read a portion, but not all, of the older posts. Not having seen the bit about your 360 crank, I'm quite pleased that the one I drew up is so similar to yours (and AlexS's) It was a real "double take" moment when I saw it! How well balanced does it seem when running?
Regards,
Ron

Offline vtsteam

  • Full Member
  • ****
  • Posts: 753
Re: Halfa, a DOHC inline Twin
« Reply #52 on: December 08, 2022, 03:00:06 PM »
Thanks Ron and Roger, so it looks like you either pre-calculate it in CAD or weigh the actual parts if you make them first. (Well I guess you don't have to use CAD, it could be done with a scale drawing and some time in the evening.)

Roger, I hadn't seen that engine either. Now more to read!  :cheers:

Steve

Offline Roger B

  • Global Moderator
  • Full Member
  • *****
  • Posts: 6138
  • Switzerland
Re: Halfa, a DOHC inline Twin
« Reply #53 on: December 08, 2022, 05:00:17 PM »
Thank you both  :) As my engine builds are experimental/developmental they tend to go on for some time.

The twin was intended to be a 180° twin with carburettor, a 360° twin with carburettor and a 360° twin with fuel injection. The 180° twin with the SU style carb was a nice smooth flexible engine and I will probably rebuild it back to this state. The vibration of the 360° version caused too many problems for the carburetted version however the fuel injected version is quite a lively little thing.

The version of the 360° crank that I made was still a little under balanced but getting the last few grams off was going to be difficult  ::)

Please note that a lot of the YouTube links are currently broken. This is being fixed but all you will currently see is the core of the YouTube address which you can copy into the normal YT format.
Best regards

Roger

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #54 on: December 08, 2022, 06:05:22 PM »
The other half of the 1144 bar is earmarked for a possible future 180º crank.
Regards,
Ron

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #55 on: December 09, 2022, 01:00:51 AM »
Continuing with the crankiness from yesterday. After the waste directly under both future rod pins was removed, I rolled the part around in the vise so the bottom of the cuts was now vertical. A rod held in the spindle was used to help with this alignment. In this case, since it's roughing work, close enough is good enough. Then the waste on that side was removed, and the process was repeated on the other side.


Then it was over to the lathe to turn the pins. I started with a series of plunge cuts using my narrow (1/16”) parting tool. Then my intention was to switch to the stiffer and wider (0.093) parting tool ground from a 1/4” tool blank. That is, until I realized that tool is not long enough to reach in as far as it needs to without a fair bit of additional grinding. After mucking about a bit with various alternatives that didn't really work, I went back to the skinny tool. With it I got the pins fully rounded off, and with a pretty decent finish to boot, though I've left them oversize for now. Although it's far too flexy to be any use in taking much off the sides of the webs, it can be traversed very lightly back and forth across the width of the pin to get a uniform finish after getting to diameter with a series of plunge cuts. I'm going to have to come up with something else to finish the sides of the webs though.




You may possibly be wondering why I have the part in a 4 jaw chuck with one jaw missing. Actually, the part is mounted between centers, the chuck is only serving as the drive dog. With the offset, one jaw comes up against the side of the bar in the direction of rotation and provides the drive. The other two are only along for the ride and are just tightened down enough to not fall out. The offset would cause the fourth jaw to hit the bed unless it were reversed. Easier to just remove it. The live center is not visible in the photos. I made it a while back with a taper matching Taig's proprietary spindle nose taper and it's pulled up tight with a 1/4-20 threaded rod draw bar through the spindle, with a collar and nut at the outer end.

Regards,
Ron

Online Kim

  • Global Moderator
  • Full Member
  • *****
  • Posts: 7863
  • Portland, Oregon, USA
Re: Halfa, a DOHC inline Twin
« Reply #56 on: December 09, 2022, 04:47:46 AM »
That's a pretty clever way to do between centers work, Ron! :popcorn: :popcorn:

Kim

Offline kuhncw

  • Full Member
  • ****
  • Posts: 232
Re: Halfa, a DOHC inline Twin
« Reply #57 on: December 09, 2022, 05:10:16 PM »
Nice work, Ron.

You are getting a lot of work out of those Taig machines!

Regards,

Chuck

Offline RReid

  • Full Member
  • ****
  • Posts: 1668
  • Northern California
Re: Halfa, a DOHC inline Twin
« Reply #58 on: December 10, 2022, 12:38:11 AM »
Thanks Kim!

Hi Chuck, and Thank you! Just trying to recoup my (small) investment I guess. :)

Not a whole lot done today, but I did get the rod journals finished, so that's something. The photos below also show the live center I mentioned in the last post.



Regards,
Ron

Offline Admiral_dk

  • Full Member
  • *****
  • Posts: 3752
  • Søften - Denmark
Re: Halfa, a DOHC inline Twin
« Reply #59 on: December 10, 2022, 12:58:55 PM »
Love your setup  :ThumbsUp:  and it looks like the process gave a fine result  :cheers:

I have seen a number of builds here where the 'Gap not Cut' is supported with anything from an kind of expander to glue - simply to prevent it (or them) from flexing while cutting elsewhere ....

Per

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal