Marks Holt 75

My next step is to hollow out the upper half of the crank case. This required three stages, first the center area that is flat, followed by the two angled sides. I plunge cut for the rough out. Its a lot of material for a small mill so it took some time. Next I made the cutouts for the center bearings, cut the slots for the bearings splash oilers and bored the holes for the cylinders and push-rods.

The center bearing blocks are of bearing bronze. Nasty stuff to work with. To lay out where to bore the hole I used a dial indicator and the mills DRO to figure out the vertical measurement. For the lateral measurement I measured from the jaws of the squishing device. (or I could have said I measured from the jaws of my vice but you guys have beat me up for that before) I then used a pointed center to locate my layout for the hole. I screwed up my vertical calculations and my holes ended up .005” to low. I keep an assortment of beer and pop cans for times like this. So from a pop can I cut some .0055 shims to but under the bottom bearing block.

Before drilling the hole for the shaft through the bearing block I drilled the holes for mounting the block to the case. And I made some very close fit dowels to hold the halves together while I bored the big hole for the shaft and cut the blocks to their correct width. The main end bearing holders were fitted with pressed in bronze bushings that fit the test shaft snugly. Using the test shaft the center bearings were located and drilled and taped for mounting shoulder screws.

The bushings and bearing blocks were fit snug to the test shaft and now need to be reamed up to the correct size for the crankshaft. To do this I made an adapter to fit over the shank of the ream. This I hoped would keep the ream in line. I reamed one outside center bearing block and the main end bearing then flipped the setup around and reamed the other end. After that I reamed the center bearing block using one of the already reamed blocks as a guide and continued through to the far end. And then with crossed fingers I assembled the bearings with the shaft in place. With fingers It turned a bit stiff with a slight bump. A little oil helped with the stiffness but the bump remained. So I put some lapping compound on the bearing surfaces and turned the crank at slow speed with a drill motor for about five minuets. After cleaning up the shaft and bearings I reassembled and the shaft turned smoothly without the bump. Run out at the end of the longest shaft end was .0032” so the end of the shaft is about .0016 out of place.




Next up, hollowing out the lower case. I need to be away for a few days but will get started when I return.

Mark T

Very nice work, Mark.

Chuck

Just went back ans started from the beginning. I will be following this one for sure. Thanks for sharing.

Time to hollow out the lower crankcase and shape the outside of both crankcase halves. So this part of the project isn't difficult to do, its just very time consuming. There were a lot of setups so plenty of room to make a mistake. I got lucky and everything went smoothly.

The drawings show some curved areas on the inside of the lower crankcase half. I opted to just do some faceted cuts to safe time. The difference is very slight.

Shaping the outside of the case halves does require some curved surfaces. I like to redraft all of the parts so I can take measurements from points I can reference. Using my drawing of the case I made a cutting chart for the rough out and finish cuts. The first rough out was with a 1/2” flat cutter followed by a .313 ball nose cutter. The finish cut was done with a .187 ball nose cutter.

This part has given me CNC envy. I have a CNC router that I built back in 1999. I occasionally do small aluminum parts on it but the 30,000 RPM spindle is way to fast. I would like to build a CNC mill but I'm to old now to justify the expense.

So there it is, just need to spend a day sanding the curved areas smooth and the case halves will be done. Now I really don't mind sanding because while beer and machining don't mix, beer and sanding do. I used a 1 inch pad sander with 100 grit paper to take the rough areas down. It actually went quickly. I followed with a .5 inch pad sander to get into the corners and some paper glued to a Popsicle stick to get into the tightest areas.

And then to give the parts a cast look I sandblasted with fine sand. The final step was to anodize the part to give the surface a tough shell. The parts were then sealed with hot penetrating oil.

Final photo of all the parts made so far assembled.

At this point I have options as to what I do next. I'm thinking the gear case(s) make the most sense, followed by the gears and cam shaft.


Mark T

Wow! Outstanding job on the crankcase. The anodizing looks great.
gbritnell

Realy cool. I also purchased Georges nice plans and i will follow your progress . I am working on a metric conversion and drawing the whole engine with Inventor.
After that i will start with my build.

Regards Michael

The crankcase turned out beautiful! Great finish.
I'm looking forward to more.

John

Outstanding !

Thanks for taking the time to comment guys. Besides my UPS driver your about my only contact with the outside world.

Mark

I really like the way you made a faux casting (my term) look on this. It looks great!

Can you give some specifics on the hot penetrating oil comment? Was this a bath or just rubbed in? I'm assuming a bath given the 'hot' comment, and if so, how long and what temperature? Thanks.

Normally after anodizing aluminum you immerse the part in a sealing solution for about 15 minuets in a water soluble sealer at about 200 degrees. I just substituted penetrating oil for the sealer. It stinks and smokes a lot so I do it outside. It gives a darker final finish.

Mark

This post is about the large gear case and the details I omitted from the main bearing holders earlier.

The only photo I have of the parts for the main bearing holders is this one where I am using my lathe as a shaper to rough out the half round feature. I had used the mill to shape the block and remove most of the material for the half round areas. When completed the parts were glued to the bearing holders with locktite.

To start the body of the gear box I used the lathe to machine detail to the back of the box. I then turned the material over in the lathe to face the other side and bring it down to the proper thickness. After taking the first cut I measured the thickness and found it varied. So change of plans, will cut to thickness on the mill. The sun went down and came up again the next morning. And I forgot about taking the part down to thickness.

The next step required a turntable. A little back story here and then I will circle back. My table is a 6” model I bought from Grizzly. It looks like a Vertex but has no name on it. On another thread “Rotary table problems” a member “petertha” provided links to two videos showing how to improve the Vertex table. My table would wander off center. Turned out the table was a very sloppy fit to the bearing in the base. I am fixing that with a bushing. The bigger problem was the backlash. Almost a full degree. Well the video showed how to adjust this. There is a setscrew that acts like a stop on an eccentric that engages the worm gear. Well my table has such a hole but there was no setscrew and the hole didn't go through the casting and was not threaded. Turns out there is a broken off tip of a drill bit in the hole. Scratching my head about that. Guess Vertex didn't want that table but Grizzly was OK with it.

So I have a crappy table and that makes the gear box a little harder to make. With so much backlash I opted to shape the outside of the box and its lid by plunge cutting. To mount the part to the table I attached a piece of marine plywood to the table and faced it with the mill. I then cut a pocket in the center of the table to the size of the boss on the backside of the gearbox. And I made two adapters for centering the part for cutting the end pockets for the smaller gears. It was while I was drilling and taping the holes for the lid to the gear box that I remembered I had not cut the part down to thickness.