Cirrus V8 rotary valve engine build 2x scale up

[davidyat]

Barry,

Finished my Oak Bookcase and can get back to the shop. Not only am I making chips, I'm also botching up the crankcase. Blew the first one. And almost finished the second one when this happened. On the C journal, even at 28 rpm on my LeBlond (1947) Lathe and turning in the cross slide by hand a few thousandths at a time, on one revolution, it grabbed the crank and you can see the end result. :wall: My retired master machinist who is guiding me, said I could have been to slow a speed on the lathe. I also did what he suggested which was to hog out a lot of material in the journal areas on the mill before going to the lathe. You can see some of the hogout in one of the pictures. The first 2 journals were no problem at all which I hope you can see in the picture. Now with all that said, is it possible to make a crankshaft out aluminum? Possibly 7075 T6 aluminum? Also, when I tried on the first crankshaft without hogging out material in the journal area, the square nose tool would really grab the crank and would scare me half to death. Can you give me any advice on how to attack crankshaft #3 (and hopefully the last). I also posted a picture of my LeBlond.
Thanks,
The Learning Grasshopper

 

[davidyat]

Barry,

I forgot to mention that I was using a 0.500 square nose cutting tool on the lathe. Then I noticed you were using a square nose much smaller and taking more cuts. Is this where I possibly made my mistake?

Thanks,
The Grasshopper

 

[petertha]

Sorry to hear about your crankshaft machining problem.
- can you describe (or show) your cutting tool?
- I'm curious about the offset fixture on headstock side, how is the crank retained in that (wondering out loud if it loosened within the fixture)
- did the outer journals cut or sound worse as you progressed away from the successful ones closer to the headstock? On one hand one would think more flex in the crank as it cantilevers, but now you seem to be getting proportionately closer to tailstock support, no?

I've seen pics where people insert temporary webs in the machines sections. I always assumed it was for minimizing distortion, but maybe part is to bulk up the rigidity as more material is progressively removed.

 

[bazmak]

Hi Grasshopper,i never had any problems.Although i show a 4mm wide
carbide tool i did use a variety of tools including a parting off tool
The eccentris bearing journals were for 12mm dia bearings and i left
the eccentric parts oversize at 14/15mm dia for strength.I roughted out everything carefully by nibbling with light cuts and taking everything down in size in stages to keep strength
The width of the webs i cut down with a LH and RH tool..Speed was between 100 and 200 rpm.Looks like you might have tried to machine one area too far
and weakend it. I took my time in stages keeping as much meat as could
Final fish very light cuts with sharp tools .5 wide tool no good try starting with a 2.5mm wide parting tool and work mainly with the edges to get almost to full witdth.If you take everything down to nom 1mm oversize then treat it as a casting to finish all dims.The 12mm eccentric dias should be done last then the shaft ends finished to size.Have attached all my photos.Hope this helps.As i said
i did not have any problems but if i remember did spend a couple of days
With collet and tailstock ctre and the 2 fixtures it ok to move the job about until the final finish. Good luck

 

[bazmak]

more photos

 

[davidyat]

Here are some pics of the tooling. The offset jigs are aluminum with the set screws for holding the crankshaft. I used a 1/2 inch square nose tool bit for my cutting the journals. I ground a little clearance behind the cutting head so to make sure I wouldn't get any interference with the shank as it went deeper into the rod journal. I hope you can also see that I went to the mill and ground out a lot of material in the rod journal areas before I plunged the square nose in. This left me with about a 5/8 inch square where the journal is. This minimized the amount of material to be ground off for the journal. When I get another blank to start, I'm going to really look at your pictures. I can understand now about flexing as I get away from the head stock and toward the tail stock. My next approach will be to make the journals first, then grind the concentrics. Also I'm going to make another set of offset jigs. On my first two learning experiences (I never have failures, only learning experiences. Learning how NOT to do it), I first ground the ends to 1/2 inch, ground out the concentrics, made the jigs to fit the 1/2 inch ends. This time I'll leave the ends more beefier, 5/8 or 3/4 inch to hopefully get less flexing.
The Grasshopper

 

[bazmak]

There are too main points to consider when machining.Is the lathe robust enough and is the finished item robust enough to withstand the cutting forces
Looking at your lathe pictures the answer to your first question is yes.However you need a sustancial workpiece to withstand the cutting forces from a .5" wide
carbide tool with very little rake.Although the lathe will take the load THE JOB WONT.I show a 4mm wide carbide tool for roughing,however you can see in the photos that i instantly started with chatter.I quickly switched to HSS with top rake and gently nibbled out the majority of the material
I did NOT machine down fully the eccentrics or concentrics but roughed out all of them one at time to nom 10mm depth of cut.Working nearest the chuck where possible and reversing the job to repeat.I then repeated to stage 2 and
a depth of cut overall of nom 15mm deep,and again repeated again to stage 3 etc reducing depth of cut all the time.The aim being to keep a max strength as long as i could to all journals. Once i had the main turning done to within 1mm i finished off very slowly and carefull with 3 parting tools
1 grd LH,1 x RH and 1 sq,just to finish the sides of the webs and dia of the journals etc
Your main mistake is the use of the wide carbide tool and milling out the meat.Use a ground HSS tool say a parting tool,good for the final depth and dont overmachine 1 web as this gives a weak point when you start another web.Break it down gradually in stages to keep max strength as long as you can.Finishing cuts should be no more than a couple of thou.As i said i took my time and spent a couple of days making sure i did not overstress the workpiece. Good luck and post photos as you go will be happy to help further
Regards Barry

 

[bazmak]

Also i should point out when machined the crankcase i bored the ends and centre to 16mm dia so could check the alignment with a 16mm dia shaft
Then i machined the centre of the shaft to 12mm dia and made and fitted the brass centre bearing.when i made the crankshaft i machined the ends to 16mm dia to turn all the journals then machined down the the end dias last.Again to keep max strength in the workpiece throuout the hogging process

 

[davidyat]

Barry,
A thousand thanks for your advice. I can now see the logic in your words. I've often been described as "A Bull In A China Shop" and my work is showing it. Taking the time with smaller cutting tools and finesse is the way to go. As I've said before, I just learned another way of how NOT to machine a crankshaft. Let's see if "Third Time Is The Charm". Again, thank you.

Dave

 

[bazmak]

take some photos and do it in 3 stages to + 1mm all round.The concentrics
finish at say 14mm dia from 40mm dia thats 13mm depth of cut.Stage 1 go to 5mm deep then stage 2 to 10mm deep then down to =1mm. do the same for
the eccentrics journals but note deeper overall.Start with the one near the chuck then the middle,reverse in chuck and repeat.Total of 7 in all. Take them all to stage 1 then repeat etc.Dont forget the centre one will be finished to 12 dia for brass bearing.The other 2 concentric can finish at 14/15mm not important.I then finished the sides of all the webs to size and width wit both LH and RH parting tools and some side clearance.I finishe the journels to size with
the square end parting tool and u cut slightly the corners with the lh and rh tools,although it was not necessary as i countersunk the big end bores in the
brass conn rods.Take your time its worth the effort and much easier on the mind than cocking one up.Guess i was just timid and lucky. Last job is to turn the shaft ends to suit bearings etc.Cant remember if i taped packs between the webs but dont over tighten the tailstock centre

 

[davidyat]

Barry,

I see you made the monthly newsletter. Your build was the one that got me started on my build. I'm taking a sabatical on the crank until I get another blank and working on other things for the build. I've managed to mate the cylinders with the block and am now working on the brass manifolds that will mate with the top of the cylinders. I've also made the decision to go with a toothed belt for the crank and the rotary valve. I've seen one work on youtube. I found this company that sells the items I believe will work for my build:
https://www.ondrivesus.com/
And I'm sure I can make an adjustable tensioning device for the toothed belt to keep it in proper tension.
The Grasshopper

 

[bazmak]

Looking great,hows it going with the crankshaft ?

 

[johnmcc69]

Looking good so far. Nice work.

John

 

[davidyat]

From my previous post, I'm taking some time off on the crank. I'm going to work on some better, stronger offset jigs for the crankshaft. Then psych myself up to tackle another crank. Then go back and read and absorb the wisdom of Barry and take a lot of time on the next crank. I've been using my time to make the jig for the rods and finishing up the intake manifolds.

Grasshopper

 

[bazmak]

Good work grasshopper.I too thought of a small toothed belt drive
but finished up using gears.I am very interested in how yours goes
should look much improved with a nice tensioner/idler pulley

 

[davidyat]

Barry,

I looked at your Locomotive blog. And NO, this will not get me started on one myself like I was inspired by your Cirrus V-8 2X build! But at the end, I see you're going for a tool post grinder. Have you started this project yet and have posted anything on it? With my problems with my crankshaft, I'm thinking maybe a tool post grinder for making the crankshaft might be a safer way to grind the journals. Your thoughts?
Grasshopper

 

[bazmak]

I had no problems whatsever turning the crankshaft so nor should you
Grinder finished but i think turning the crank is the best way
Just take it slowly in stages

 

[davidyat]

Grasshopper here. I've been busy with other projects and a trip to California for income taxes. Moved out of CA and am now living in Indiana just 8 miles from Turn One at the Indianapolis Motor Speedway. Yes, I have my tickets for this year's 500. Hope my pictures come through. First off, this Saturday, I'm going up near Detroit, Michigan for the NAMES (North American Model Engineering Society) Model Show. Here is their website:

http://www.namesexposition.com/

I'm hoping to get a lot of information. They say the show has 30,000 square feet of exhibits. At this stage of my machining learning process, I will need all the information I can get. I'm hoping to meet a lot of macinists with more knowledge for me to absorb.
I've managed to make the intake manifolds. I'm going to use brass compression fittings for the manifold and the block. That way the air tube doesn't have to be exact in its' length.
8 Pistons
8 Rods ready for finishing
The 4 inch rotary table with the jig for the rods
The new offset jigs for the crankshaft with 0.750 inch holes for the ends of the crankshaft. I'll turn the ends down to the 0.500 inch I need for the sealed roller bearings when the crank is done.
The crank with one end turned down to 0.750 inch. Working on the other end.

 

[davidyat]

Well I'm getting ready to turn my THIRD crankshaft. But first, I did go to the NAMES Model Engineering Show near Detroit, Michigan. OH, MY GOD!!! I was in heaven. Some of these more experienced machinists were to be admired. And they were so polite and wanted to hear of anything you're working on and didn't talk down to you no mattrer what your experience. I did spend 1/2 of my time going through the vendors and found a good amount of tooling I could use. Let's see how many photos I can get in one reply. I highly recommend this show to any machinist. And also if anyone is near San Diego, California, I also recommed The Joe Martin Craftsmanship Museum. Here's the URL: https://www.craftsmanshipmuseum.com/

Grasshopper

 

[petertha]

Nice pics. Did you happen to catch what radial is in pic-2 & builder?

ps - good luck with the crankshaft.