Little Demon V8 - helpful hints (hopefully)

[Carbuilder]

Time to make some really tiny parts. But first, how to part them off without losing too much material. I don't want to make a part that is only .052" thick and then remove more than that parting it off. So...

I took a piece of broken bandsaw blade, .025" wide, and cut/ground it to fit in the parting tool holder. Made a tapered piece of aluminum to clamp the blade in place. It is a bit flexible, but only needs about 1/4" protruding.



To make the spring retainers I started with 1/4" rod and brought it to the correct diameter for about 1". Drilled it as required to the same depth.



Used a 3/16" end mill to produce the counterbore in it, .020" deep.



Then used my little parting off tool to produce the groove in the backside, .030" in from the end and about .125" dia. The parting tool worked great. I didn't slow the lathe down much from normal machining speed for this material/diameter.



Zero'd the dial and then moved it .022" to the left and parted it off. Before the parting was done I cleaned up the edges with a small file to minimize the hand work after.



Then just clean up the end that is still in the collet and repeat. The cut-off part needed a little cleaning up since even with very light cuts with a sharp cutter the inner hole does tend to close up a bit from the material rounding in from parting. But doesn't take much to clean up, other than trying not to drop it or file my fingers.

It is difficult, for me anyways, to get a decent picture of tiny parts like this.



Rick

 

[Arild]

Do you know if anyone tried to cast all the aluminium parts for this engine?

 

[Carbuilder]

Not as far as I know. Not sure how much of an advantage it would be with so much machining needed on each part. maybe someone that does home casting will comment.

 

[Carbuilder]

On to the rockers.

I probably spent more time trying to figure out the best way to make these than with any other part. They have to be machined from 2 sides and are very small and difficult to hold. So here is what I did.

CNC machined them in a block of material a little thicker than required. I didn't want to machine them with tabs holding them in place like I usually do, since they are so small.



Then, borrowing an idea from another thread, I put epoxy in the machining. I didn't want to waste too much epoxy, so didn't fill it up all the way, just enough to hold the parts as I machined from the back side.



Then flipped it over and machined to final thickness:



I popped the parts out and pulled off the epoxy. Then marked the parts for the threaded holes. There are 8 right hand and 8 left hand...plus a spare or 2.



Drilled and threaded, and a fixture plate drilled. The idea is to put the rockers on the fixture, attaching with the threaded holes in the rockers through clearance holes in the fixture with screws from the bottom.



With the rockers screwed onto the plate, aligned with a square as each was tightened down, the small holes are drilled from the underside of the fixture plate through the rockers. This hole is used to put a 1/16" pin through each rocker to keep it from rotating. The hole will be in the middle of the rocker slot, so will be removed later.



Pins installed and rockers machined again.



So now I have a bunch of semi-finished rockers.



My concern at this point is the strength of them....or lack of it. I know they must work, but some areas are pretty thin. The slot still has to be machined where the small holes are. That slot leaves .020" material thickness between the slot and the oval hole. .020" thick aluminum can't have much strength. Then there is the spring retainer counterbore that has to be put in the same area, further reducing the material.

To be a bit clearer, this is the material that is removed when slotted:



I'm wondering about cutting the retaining groove in the valve a little lower (.020"?) and maybe making the valve stem a little taller (another .020"?), that will drop the spring retainer .040" further from the bottom the rocker, thus avoiding the need to machine the spring retainer clearance in the rockers (maybe). Yes, that will change the valve geometry a little, but enough to matter?

Not sure yet how I'm going to machine the slot. Bandsaw it in and then cleanup with a file? Not sure I like that. Come up with a fixture and machine with a 1/16" end mill with the rocker held vertical?

Rick

 

[michael-au]

good work on the rockers
looks like the epoxy idea works good

 

[Carbuilder]

good work on the rockers
looks like the epoxy idea works good

Yes, something to keep in mind that may come in handy. I used a clear JB Weld that I had. It didn't seem to cure really hard (could have been me not mixing the proportions perfectly), but that may have been an advantage. It held the parts in place fine, but also pulled off fairly cleanly without using heat.

 

[Carbuilder]

Repairing a camshaft.

I've roughed out the cam for the Little Demon. My plan is to CNC it, but I first machined the ends down to the rough final diameter and cut the spaces between the lobes. I did mess up one space between lobe groups that resulted in one lobe being undersize in width, .10" as opposed to .155". The others aren't all perfect, but are a lot closer.



It would probably work fine as-is, but it bugs me. So I thought I would repair that lobe. The first plan was to machine a thin piece and silver braze it in place. I was a little concerned with distorting it, but that may not have been a valid concern since it would all be machined afterwards. But JB Weld is generally regarded as being able to glue engine blocks back together (I actually did use it once to glue a piece of a 5L engine block back on after I cut it off and then wanted it back on). So, epoxy it is.

I machined a piece of the same steel a little thicker than I needed. Of course I had to make 2 pieces and then cut them to get this:



JB Welded in place:



Cleaned up on the lathe after curing:



Really pleased with how it came out.

Rick

 

[michael-au]

Nice job on fixing the came, save a lot of time and material

 

[Carbuilder]

I'm kind of nervous about putting this on the CNC mill and pressing the start button. Really don't want to see it messed up, so I'm trying to sort out some other issues with the programming first. I'm close to pushing the button though!

 

[michael-au]

I can understand the nervousnes

looks like I have to get a new controller for my mill, giving me problems with the Y axis, from what I have read there is a lot of people that have hade the same problem,
Im leaning towards the Masso controller and doing away with the computer

 

[rrocky]

 

[raveney]

Do you know if anyone tried to cast all the aluminium parts for this engine?

Lost Foam cast an aluminum tunnel ram. Thread here
http://forums.thehomefoundry.org/index.php?threads/miniature-tunnel-ram-intake.2092/

 

[stevehuckss396]

Cool thread but you have to be a registered member to blow up the photos big enough to see anything.

 

[Carbuilder]

Didn’t know that. I’ve been putting them as thumbnails so they would be in the text. I just logged out and had a look and could see them all fine. Should I be doing something different with the pictures?

 

[stevehuckss396]

Your pictures are fine! I was refering to the photos in the miniature tunnel ram thread I can see them but they are tiny and I cant blow them up as an unregistered guest.

Your thread is great. Don't change anything. I'm reliving my youth looking at it. I't been 10 years.

 

[Carbuilder]

When I log out on my iPad or desktop Mac, I can see and enlarge them fine. Does it somehow know I am still a member? Don't know what else to do with them unless someone advises me.

 

[Carbuilder]

Your pictures are fine!

Oh, OK. Good.

 

[Carbuilder]

Quick way to get the camshaft blank ready.

When I made my first camshaft blank (which I ruined when machining the lobes), it took quite a while to machine the grooves that are between each lobe. I used a parting blade that I ground thinner.



I used a collet chuck and extended the blank out as the grooves were cut (cutter looks like it has more taper than it actually did).



This took quite a while, broke off the end of the cutter once, and was not a fun operation.

I've gone through a number of test pieces in sorting out an issue I had with mach3, but kept thinking of how to speed up that process.

The first thing I did was blue the whole length, put a scribe in the tool holder, and use the DRO to move it to each lobe position. You could certainly do this without the DRO.



Now, how to cut all those .0535" wide grooves? Would you believe I went from the above picture to this in about 4 minutes?



You would? They still need to be cleaned up a bit, but that should be a lot easier, faster, and less clenching than using a parting tool right from the start. So how did I do it? With this:



The grinding blade in that tool is .040" wide. I just held it by hand and visually lined up the blade with the marks. I ran the lathe slowly backwards, the blade forwards, and it cut nicely and quickly. That is my favourite tool for cutting off small bolts, music wire, fibreglass panels, hardened stuff....super handy.

The grooves are more or less a bit under the final width required (I was just holding the tool by hand, so ended up with grooves closer to .050" wide). I'll grind a parting blade to about .053" wide and use it to clean them up and take them to the correct depth.

I was really pleased/amazed that it worked so well.

Rick

 

[michael-au]

learn something new every day

 

[Gabe J DiMarino]

After cutting the lobes in the wrong place on my first cam I blanked out a second in 1.5 hours .Cam material is 420 stainless cut it with a high speed tool bit ground to .050 thick .