Supporting > Engine Ancillaries

Building the Minimag

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Bogstandard:
This block seems to have taken an age to get to this stage, but what you must remember, I am now a very slow machinist and builder, so most reasonably experienced people could do this whole block easily in a full working day, if you have things organised.

This stage is now to get the block into the correct shape to accept the coil, which is sitting on top. If you look very closely, you can just see the layout lines for the required cutout.




The usual thing, straight down the middle with a big cutter, not quite to the bottom of the required slot, then go to each side in turn.




Just reaching the second side.




And this is what it turned out like.




This next bit is the final shaping of the block. The level bit is done first, then the angle.




Because the lamstacks were not quite flush or below the side faces, I used an extra set of paras, one either side, but not as far forwards as the lams, So allowing the block to be held rigidly. The horizontal cut was then taken to depth and the correct distance in.




Again, because I don't have a swivel base on my vice, I can't do the cuts as shown in the instructions.
Because this angle isn't super critical to the build, I continued to hold the block as before, with 4 paras, but eyeballed the angle and made sure that the bottom corner of the block was resting on both lower parallels.




Using a 10mm ball nosed cutter I cut up to the line by about 2/3rds down from the top. Then once the line was reached, I continued cutting straight down until it was almost at the horizontal face. Once it was taken out of the vice, I blended the radius in to the horizontal face with a round file and a bit of emery cloth.




That is all the cutting that is needed.
As can be seen from this side shot, the coil can now fit where it should.




And another shot from the front.

The holes in the coil were then spotted thru so that the holding screw holes can be drilled and tapped.




Even though the block is to shape, lots of holes need to be drilled. Their positions are all shown on the plans.

These holes thru the 'ears' are for a couple of grub screws, that if you haven't got quite a tight fit of the coil lams to the side lams, the coil lams can be forced down so good contact between the two is made.

Because I am a belt and braces person, even though I have good contact between them, I am going to use these as well.




The next job was to pick up the two spotted marks and drill the holding bolt holes to depth.




These four 2mm tapped holes are for a cover plate to fit over the rotor. This is optional, but I think it is a necessity, purely to stop bits sticking to the magnets in the rotor.




Then finally, the four magneto mounting screw holes.




All the holes were tapped to their correct sizes, and the coil checked for fit.
This block isn't quite finished with yet. It needs some bits making on the lathe and fitting, then the few remaining holes can be drilled. But other than that, this is that very complicated looking bit finished, just by carrying out some relatively simple machining exercises, done in a logical order.




Onto the lathe next time.


John

Bogstandard:
Just a little bit this time, but still progress.

I will just make a point about a couple of things.

The materials that have been supplied in the kit have been spot on for the job they have to do, and up to now they have machined beautifully, especially the aluminium, no tears, rips or picking up. It has been a joy to use.

The second concerns accuracy. For some of the parts made in the lathe, good accuracy IS required between certain ones, otherwise things will lock up or not, depending on what is required. This is especially critical on lengths of parts. So allow extra time just to make sure that things are really spot on.


I am now starting to do the lathe work, which concerns mainly the spindle, points operating cam and bearing fitment. The first piece called for is a spacer to go between the two spindle support bearings.


The instructions called for opening up the centre hole to a certain size with a drill and that is the job done.




Unfortunately, I can't be like that, so I opened it up to one size smaller and finished it off to shown size with a boring bar. It only takes a few minutes longer, and the surface finish is much better.




The outside size was turned down until it fitted into the thru hole with a nice sliding fit, not too tight as Loctite will be used, and that requires a bit of space to work in.




The spacer was parted off and brought to exact length.




The spacer needs to be fitted from the front face exactly the width of the bearing. So what I did, was to put the block face down with the bearing pushed all the way to the bottom of the thru hole and the back end of where the bearing sat was marked up with a felt tip.
The front bearing remains free to be taken out, so I had to ensure that no Loctite could get to it. By putting the drops of Loctite further in from this mark and assembling from this front side, the bearing will be safe.




The spacer was put in first, followed by the bearing, but not fully inserted. By pushing from the back of the mag block until the front hit the 321 block ensured that the bearing and spacer were in their correct positions, with the bearing flush with the front face. Another 321 was pushed up to the back face to keep things steady until the Loctite had done it's work, in this case, 5 minutes.




Next came the cam, very easy to make, but this is one component that does need to be made the correct length for it to adjust correctly.

The centre was first drilled then opened up with a 12mm reamer.




The outside was brought to size, then parted off and brought to length.




The cam blank was then tranferred to the mill using a square 5C collet block, and the flat face put onto the outside. There are lots of simple other ways that this could be done, so no worry on that score.




The block was then rotated 90 degs and the hole for the retaining grub screw drilled in the correct position.

It was then transferred back to the lathe to have the outside polished a bit and the flat blended a little into the side curves.




Once the grub screw hole was tapped out, the cam was finished. The instructions suggest that if you wanted to, you could case harden it. I will make that decision when I have made all the parts.




A bit more lathe work to follow.


John

swilliams:
This is really nice John. I could make good use of this kit once it comes on the market. Any idea about its suitability for multi-cylinder engines? Would there be a limit on how many cylinders it could handle?

:cheers:
Steve

Jasonb:
Steve, its been on the market for some time now, Bogs is just copying an earlier thread from elsewhere

http://www.minimagneto.co.uk/Products.php.

Its a shame they don't think it suitable for engines over 50cc (though they do show it running a lister) as in my view its too bulky for the smaller engine and needs something of a decent size if its to look anything like scale. There are other designs about for magnetos of about half this size which look a lot less out of place on a small engine

J

swilliams:
right - Thanks Jason

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