Possible Homemade Tool... Or Possible Fail

[90GTVert]

I sketched out some ideas and decided that I would give making a case cutting tool a go. IF it works, it'll be to clearance horizontal Minarelli crankcases (at least clones, not sure if the good stuff is exactly the same) to fit stroker cranks. That's a big if. I may fail and make a fool of myself. If that's how it goes, then hopefully I'll learn something along the way.


I started with a piece of 4130 steel 1" round bar, cut to just over 8" long. I had 2 plans in mind, one of which could use substantially less steel, but I suspected that it wouldn't work as I'd like. Either plan needed the same first cut, so I could revise if needed mid-build.

I turned one end down to just under 20mm in the lathe, because a 6204 bearing (that the Mina uses for the crank) has a 20mm ID. I did not want a press/tight fit, but not a lot of slop either. I forget where it ended up. I kept taking it off of the live center and checking with a bearing to see how it felt.

Once one side was done, I dropped it into a case with a new bearing in it. As I expected, it wobbled quite a bit. A little from not being a tight fit in the bearing, but it mostly seems to be because of movement of the bearing. By the time you get a few inches from the bearing, the play is significant. That kinda sucked, because the first plan was the simple one that involved considerably less work. I guess a case half could be secured to a drill press and it may work that way, but I was hoping for something closer to a standalone.


Oh well, onto plan B. I put the piece back in the lathe and continued working on it. I left around a 3/4" section near it's 1" original size, and then cut another section to just below 20mm to fit a bearing. Then I cut the end down to a little below 1/2" OD so it could be chucked in a drill.






Then I had a section to fit a bearing in the case and a section to fit another bearing, but nothing to hold a second bearing. I had a somewhat simple idea, using some steel that I had around. I planned to use a piece of 1/8" thick by 1.5" wide flat bar to hold a bearing above the cases. 1/8" seemed like it should handle the stress it would need to, especially since it's all that I had around. Before I worked with the steel, I made a template from a piece of a folder to make sure I got it right or at least close. That let me press/tap on the folder to get outlines of holes and the shaft of the piece that I had just made with the lathe.




I drilled the middle hole to 1", because I had a 1" bit and I thought that it should provide sufficient clearance
for a 20mm shaft to pass through.




That worked fine for the 20mm section, even though I got a little off center with the shaft somewhere along the way, transferring or drilling. What I realized then though, was that I could fit the larger section, which I hope to hold a cutting tool, through the hole as well at that size. That would give a little extra travel if needed. I used a carbide burr in the Foredom to open up one end of the hole enough to give more clearance around the larger section of the tool.




The burr made the perfect shavings to stick into my hands. I was fine till I brushed off my shirt. Then I ended up using needle nose plier to pick out at least 50 metal pieces. I've seen someone stick their hand onto a mini-cactus and have to have spines removed and it was quite similar. I'd think I had them all, then grab something else and feel some sticks. Back to the pliers.




Back to the parts, I had a plate that worked. Here's the best I could do of a mock up at the moment.






As you can see, I will need something to hold a bearing on the steel plate. I have a piece of steel pipe here with a 35mm ID and thick walls. I hope to cut it to a 37mm ID and then weld it to the plate. I've ordered a 6904-2RS bearing. That's 20mm ID just like the 6204, 9mm thick, and 37mm OD. I wanted a ZZ (metal shielded) bearing instead, but the 2RS was $4 shipped and the ZZ was $10 and I got cheap. I also ordered a 6204-ZZ so a shielded bearing can be used when cutting. I don't plan to make it slip in and out like a dummy bearing. It will be installed normally, because I'm afraid the dummy bearing could spin and mess up the bearing seat in the cases. If there's enough friction to spin a normal fit bearing, then something has gone wrong.






The plate won't match for the small case half the same way that it fits on the large half that it was made for.




It does match when flipped over though. I can make another if need be, but I think it may work alright if the bearing is on the bottom of the plate for the small case. Both sides will need some spacing to work, and the small side will have more room for spacing without needing a longer shaft since it's more shallow.




I haven't done any machining for a cutting bit yet. I wanted to have the bit in hand before messing with it. I ordered this boring bar last night because the cutting tip protrudes away from the tool and it's 3/8", which is the largest I wanted to go. I think the cutter will need to be able to cut lower than the section that it's in, even though I'll try to get it drilled to be at the bottom edge. The 6204 bearings can sit proud above the floor (actually side) of the cases, and also I wouldn't want the bar scraping the cases to do the cutting at the bottom if at all possible. I think I'll cut the 3/4" long section shorter too, so it will give more travel.




I think this thing may be awkward to try to use, because it may prove difficult to control a drill's movement. I thought about maybe finding a spring that could be placed between the bearing in the case and the bottom of the cutting section, but then that would limit travel. If it's a problem, maybe I could cut a groove or grooves for a snap ring in the top 20mm section and use a ring to hold a cap/washer so a spring could fit between it and the top bearing or plate. I'm not really sure how much difference that would make or if it would be good or bad or how or if the tool works at all right now though.

So there's what I have so far. It'll take a bit to get the parts and get the other work done to see if it's a fail or not.

[spaz12]

Can't wait to see how this turns out

[FrankenMech]

You may be able to find a local power transmission parts distributor to walk in and buy bearings. I use IBT which is less than a mile from me. Cardboard or sheet metal circles can be used to help shield open bearings.

www.ibtinc.com/

Some way to control the drill motion is required. A drill press is the obvious choice. Unfortunately a hand drill will result in disaster.

Have you thought about using a hole saw with a pilot bushing through the bearing hole and chuck it up in the drill press? Hole saws usually have some runout but sometimes that can be an advantage.

[190mech]

I gave bunch of thought about this a few years back,,was going to support the shaft from the CVT and iggy cover flanges to have an open work area while cutting the crankcase..Pondered on just how to do the cutting also,maybe hacking up an old 50cc crank wheel and mounting the cutter bit in the side(ruled that out due to imbalance and hard material),,or perhaps a fixture to mount a die grinder to the center shaft(thought that would be hard to adjust and control),,soo the ideas faded away,,Hope your project does work as many folk would build bigger motors if they could have an inhouse way to machine a case!

[90GTVert]

I knew there was a tool using the first part of my idea already, the simple one just supported by the bearing in the case. I used to watch DioSpeedDemon years ago and remembered him having one for his Honda strokers. That's where the first part of this came from, but I expected that I wouldn't like that much play. The tool that he bought does seem to work for him though, sorta.






I don't really see why not having a specialty tool should stop anyone from building a stroker. I've done quite a few with a rotary tool / drill and burrs and sanding bits. Gotta break those out anyway to match up the rest of the cases. If this tool doesn't work, I don't see myself caring enough to keep working for a method since I already have one that works and doesn't require terribly expensive tools. A dremel and some bits would be as cheap than this thing anyway. The steel, bearings, cutter, tools, and especially time into this so far have made me understand a little better why these things are expensive. I've got at least $50 into this, plus a lot of time standing in front of the lathe, plus hacksaw, and drill press. More time to come, plus welding and some threading. It's usually $150-200 for the tools out there to cut the bore for the cylinder. Can't say I've seen any crank tools for sale. For a DIYer that doesn't want to or can't build a tool, that money seems more fair now. Not that I believe for a second that big companies need to charge that much to mass produce tools, but you sure can't slap one together quick and cheap (or at least none of us has done it yet).

oldgeek did try to build a tool that let you rotate a rotary tool. Unfortunately the pics are gone, thanks to photobucket.

You could get a machine shop to do cases. I had my first stroker done by a machinist. He cut the crank down a little (not usually needed) and clearanced cases and it was $280. Also put a small hole in the case in the corner between where the part being machined and where the bearing sits meets that I had to JB weld. Never did that again. I didn't get an itemized bill, so I don't know how much was the actual case cutting. He said the cutting was easy enough for him, it was all the time getting it set up that drove the cost up, as tends to be the story with this sort of stuff. He was fair on prices generally too. I had him do a head for me as well. Specified a cc and handed it to him. $20 total. From my experience messing with heads after that many times, that's super cheap for the time involved cutting and checking cc and cutting more and checking again.

[aeroxbud]

Very interesting project.

[190mech]

I too agree that a rotary burr and patience is all thats needed..Seen here a few folks mention fears of messing up a good case with a die grinder,,my thoughts are case cutting with a burr is safer as you tend to stop and check progress whereas a boring tool set up improperly can chew up a case in one turn!Quite a few high end builds have been built here with a lowly dremel and burr..I really like to slow it down even more and use a corded drill and a 1/4" shank burr like this one;
www.ebay.com/itm/SA3S-Cylindrical-End-3-8-Carbide-Burr-Bur-Tool-Die-Grinder-Bit-1-4-Shank-NEW-/381330789889?hash=item58c9161601:g:VLgAAOSwjVVVpsJI
With a bit of lube(soapy water or wd40),the cutter does cut fast and is easy to control..
Come to think back on it,I abandoned the idea due to the ease of hand cutting cases outweighed the technical challange of building a 'tool'...

[90GTVert]

You won't get a concentric and consistent case with a rotary tool/drill and a burr freehand, unless you are some sort of tool wielding deity. How much does it matter though? A smooth enough finish can be attained with large flap wheels in a drill to finish. The main thing that sucks for me with freehand work is the time and amount of aluminum dust.

If this fails, I won't be devastated. It would be cool if it works though.

[190mech]

Set up time is a killer on a vertical milling machine,takes me 6 hours of steady work to cut a set of Mina cases for the crank and cylinder..Bet it takes less time with a die grinder..A super precision cut and finish is not needed in this work,chip and dust control are a big factor though,I carry stuff out in the yard when heavy hogging is needed,plenty of fresh air outside!

[oldgeek]

Aug 27, 2017 6:26:14 GMT -5 90GTVert said:

oldgeek did try to build a tool that let you rotate a rotary tool. Unfortunately the pics are gone, thanks to photobucket...........

I was finally able to get all of my pictures downloaded from PB, I hopefully will get all my photo links restored as life allows. I dont know why I should bother though, I suspect the same thing that happened to PB will eventually happen to any other host we use.

The final tweak on my rig was a bigger rotary tool (1/4") and cutter. It made a huge difference in ease of operation and I cut the crank area on two sets of cases in less than an hour each.
Old rotary tool

This picture shows the larger rotary tool.


I also made a super simple router based throat cutting tool from four spacers that fit in the cylinder stud holes and a flat aluminium router guide plate with an appropriately sized hole cut in it for the throat that allows for the offset of the cutter. I used a router attachment for the 1/4" rotary tool and a very small sealed bearing from the hobby shop. The bearing fit perfectly on the cutter shaft, and rides on the inner edge of the throat hole in the flat plate. The real chore for me was getting the appropriately sized hole cut in the router guide plate.
49ccscoot.proboards.com/thread/17936/throat-cutting-tool-horizontal-minarelli

[AtariGuy]

Following...

[FrankenMech]

That video shows the problem with using a hand held drill and a single point cutter. The cutter digs in and bogs and gouges. An interrupted cut just makes it mega worse. That is why it is worth buying a drill press for your shop. They will pay for themselves many many times over.

I mentioned using a hole saw and a pilot bushing in a drill press. Use a piece of 1/4" drill rod instead of the pilot drill bit in the holesaw. Make a pilot bushing on the lathe with a 1/4" hole to fit the bearing opening. Use a slightly undersize hole saw and tweak it a little 'oval' to adjust for the desired clearance size if necessary.

50mm = 1.969"
52.5mm = 2.067"

A 1-7/8" (1.875") holesaw or a 2" holesaw may do the trick since they usually cut oversize anyway due to runout of the welded blade. They are cheap and can be purchased with or without the arbor if you already have one. One can reduce the runout with careful use of wood blocks and a hammer or by selective removal of teeth. One can also increase the runout with careful use of wood blocks and a hammer.
www.homedepot.com/p/BLU-MOL-1-7-8-in-Bi-Metal-Hole-Saw-530/205683525

[90GTVert]

Interesting idea. I have never liked hole saws for metal, but then I have only hand drilled with them.

Just for reference, the strokers usually need something like 80mm (3.15").

[FrankenMech]

His video only mentioned the two sizes.

Try a 3-1/8" holesaw:
www.homedepot.com/b/Tools-Power-Tool-Accessories-Drill-Bits-Hole-Saws-Arbors/3-1-8-in/N-5yc1vZc9cmZ1z0sjbi

Holesaws work well in aluminum with kerosene as a lube.

Size 'adjustment' can be checked by drilling part way through some scrap 1/4" aluminum plate and measuring the result.

I use holesaws for metal all the time but usually with a drill press. I have used a hand drill many times though. The last bit can be a bear if the drill motor is not perpendicular. Slow, light pressure, and care is required. Cutting oil helps in steel. I often stop when it breaks through and tries to grab and just knock out the rest and use a file or dremel tool to clean it out.

[90GTVert]

Here's the update on the tool. Wanted to make sure the "why" was covered for anyone not used to strokers too.





I'll get the specs I mentioned in the vid and more pics up tomorrow most likely. Tired of staring at the screen ATM.