Chevy V8 Scale Engine Plane

[davidyat]

Retailer,
You make a good point about removing material at the mill and then over to the lathe. What scares me are those squared off, interrupted cuts. In my short learning experience, no matter what cutting tool I use, narrow or wide, there is more chance of the tool grabbing that square end and twisting the part. It takes much longer doing the turning without removing material, but I have the time now that I'm retired and I seem to have a lot less problems.
Grasshopper

 

[editor123]

I was practicing making a crankshaft out of aluminum 6160. Sequence was to do the rod journals first then the mains starting from the front and going to the rear with the rear driven and the stock between centers. I milled out much of the excess but only for the journal I was working on. Got the 1-2 journal done without drama. It grabbed on the 3-4 journal, bent at the 1-2 journal and spit it out.

Is aluminum too soft to try this or was it just lousy technique?

View attachment 110806

You need to make a series of tube stiffeners that can be clamped on the bar stock diameter. Use worm gear hose clamps to hold the stiffeners on the workpiece if you cannot weld tabs on the tube for clamping screws. The tab approach is better and stiffer. You should also mill out most of the metal before you put it on the lathe. A great time saver and you don't end up making interrupted cuts.

Pictures from Issue # 30 of an article in Model Engine Builder on making multi-plane crankshafts. Note the special cutting tool.

Setup for milling out throws before using a lathe to finish them.

 

[SailplaneDriver]

What worked for me when I was making Bazmak's 2 times Cirrus Compressed Air V-8 and botching up 3 cranks, was to do the mains first. Then with the crank in the offset jigs, using a parting tool (about 0.125 wide) to start on the rod journals. Start from the tail stock and work on the journals towards the chuck. After each rod journal is made, make some biscuits to slip into the rod journal space that you just made rather snugly. Then when you go to the next journal, give a little snug pressure on the off set jig in the tailstock with the biscuit and this should give you some stability. It's time consuming with the cut off blade, but you shouldn't twist another crank.
Grasshopper

What do you mean by "biscuits"? Are they spacers to minimize the flex when you crank the tailstock in?

 

[SailplaneDriver]

Quite a few forum members (me included) find that if the bulk of the metal is machined away in the mill there is less chance of a disaster in the lathe.

I did mill away excess but only for the journal I was working on. That way the stock from the driven end was solid and would not flex. It is more time consuming since you have to remove the stock from the lathe and take it to the mill, tram it in and mill it.

 

[SailplaneDriver]

editor123, I like your idea of stiffeners. I thought of something similar using worm gear clamps and sheet stock but a tube would be much better. It also means I can mill all the journals at once since the stiffeners will provide the necessary support. Welding or soldering on the outside looks time consuming. I'll try the worm hose clamps first since they would be faster.

 

[SailplaneDriver]

I bought a 30" length of 1" schedule 40 pipe and a 10 pack of worm hose clamps. The pipe has an internal diameter of 1.049. I had to cut about a .200 slit at the weld to be able to get it to close down to a bit below 1". I made three lengths: 2, 3 and 4". Hopefully those will be enough. I managed to squash the 2 and 3" down to where they will grip the 1" OD of the crank by squeezing them in the three-jaw so they would be reasonably symmetrical. I don't have enough leverage to do that to the 4" so I resorted to a thick piece of paper. Looks like it will work. I'll try it tomorrow on the almost straightend bent piece to see how they work.

I screwed up the threads on three of the clamps by overtightening them; they don't have enough strength to compress the pipe unless you deform the pipe somewhat first. I put some scrap underneath them to allow them to still work on an undamaged portion of thread.

 

[davidyat]

What do you mean by "biscuits"? Are they spacers to minimize the flex when you crank the tailstock in?

That's exactly what I mean by "biscuits". Spacers made to fit into the web you just made for the rod journal. Mill a piece of scrap, work to get it to fit snugly with hand pressure into the rod journal space and when you move your live center into your offset jig at the tail stock, a small bit of pressure will lock in the "biscuit" and you then lock the tail stock.
Grasshopper

 

[davidyat]

Found the images I was looking for. Crank (when I was working on the mains) with the biscuits installed and the crank. Pressure from the tailstock usually keeps the biscuits steady.
Grasshopper

 

[SailplaneDriver]

Broke the crank in two this time. I had so much stickout of the parting tool that it was just slightly above center height, best guess around .020. Worked fine until I got to a finished diameter of around .300 where it grabbed and twisted the end off. I need to either reduce the stickout or cut a chipbreaker into the parting tool to reduce height. If I am having this much trouble with aluminum, I hate to think what will happen when I go to steel. I'll practice some more with the aluminum remains to see if I can get better at this.

 

[davidyat]

Don't know if this could work for you. Build up a crankshaft. I did it on a 2 cylinder, 1 rod throw with 2 rods and it worked just fine. Let's see if I can cut and paste some photos. I just drilled 2, one half inch holes (reamed) 1/2 inch off each center into the rectangular pieces. Pushed the 2 rods through that way everything stays in line. Silver soldered (with 53% silver solder, very expensive but worth it) everything together, then just machined it out. Ended up with only 0.006 thou run out at the ends. After installation with ball bearings at each end, it turns like butter.
Grasshopper

 

[retailer]

I made up an offset machining holder for my crank - have a look at this post https://www.homemodelenginemachinist.com/threads/first-ic-engine-design-and-build.31266/ and the second page shows how it was used, it allowed me to do all of the machining right up next to the holder or chuck.
While it did not work 100% how I had intended it to it was a reasonable sucess, the main downside was lateral play of the crank in the holder, while I couldn't feel any play it turned out that I was able to detect the play with a DTI as the grub screws were tightened down and the bigend journals ended varying in size by a few thou, not a disaster but also not made to the design size. I found it was better to move the cutting tool at a steady pace from side to side while at the same time feeding it in only a few thou at a time.

If I ever make another multi cylinder crank I'll look at making a set of vee clamps machined up from angle iron - a length of vee stock clamped with exhaust type c lamps to each side of the crank I envisage that the vee clamps will need to be custom made in pairs of varying lengths so they can be clamped one each side with exhaust style c clamps. If you ignore the bad perspespective of the pic I quickly drew you will get the idea.

Just a thought on the material you are practising on maybe aluminium while it is soft does tend to gall up on the cutting edge of a tool and in addition possibly is just not strong enough and you might do better with an easy machining type of mild steel. I made my crank from an unknown grade of steel described by the seller as either 4140 or similar to it.

 

[SailplaneDriver]

davidyat, I'm not sure your method for a built-up crank would be practical for a multi-plane crank. Steve's drawings have an option for a built-up crank and it looks more difficult to build without runout.

retailer, I like your offset holder. I tried making a clamping offset holder with a recessed square for indexing. I turned it with a 1.00 spigot so it coud be used in a 1" collet. It doesn't work well in practice. Probably needs some refinement.

 

[johnl]

Try making a practice crank out of 12L14 leaded steel.

 

[SailplaneDriver]

I put the crank aside and decided to work on the rest of the parts for the heads

 

[SailplaneDriver]

I vehemently hate the rocker arms. They are tiny, difficult to hold, require many many operations on different planes and are fiddly. My attempts to set up a production run resulted in about 2 out of 36 close to spec. And I thought this would be a good break from the crankshaft.

 

[stevehuckss396]

The rockers are hidden so there is no reason why you couldn't simplify the design.

 

[retailer]

What ever happens don't give up - keep at it, you will get there in the end.

 

[SailplaneDriver]

Hey, Steve. The problem is not the design, it's my skills. I'll keep at it until I get a good set. Hopefully that will occur before I pull all my hair out. You have to admit, they are fiddly little bits.

 

[stevehuckss396]

Make some kind of fixture to hold them. Do as many operations that are possible. Doesn't have to hold mare than one but it might make it easier if you do.

 

[davidyat]

Sailplane,
I had so much stickout of the parting tool that it was just slightly above center height.
My machining mentor taught me a simple method that has been working for me. Take a 6 inch stainless ruler, run your cutting tool to the work, put the ruler in between the cutting tool and the work with very little pressure holding it. If the top of the ruler bends away from you, you're too high, straight up, your probably at center. I always see if I can get the ruler to bend ever so slightly towards me. Then I know for sure, I'm below center.
Grasshopper