Another Paddleducks build log

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bogstandard:
That is really coming on well Tim.

As it said in the plans about the holes for the rods, it needs a little 'fiddle' factor to get it to move, but now you have got it, you should have no more trouble with it at all. Once you have the engine running, if you are very careful, you can in fact slacken the rods off slighty, and the engine will set the rods in it's own perfect running position, then tweak them up again while it is still running.

Once you get this engine up and running, it should give you the confidence to take on almost anything.

John

spuddevans:
Thanks John, it did take a bit of fiddling, but it got there in the end.

Today I got started on remaking the topcaps, this time out of brass.

I started with a chunk of 22mm brass rod in the 3jaw to which I trued up the end and turned as much as could be reached down to 18mm.

I then mounted my ER32 chuck and reversed the brass rod into it and turned the rest of it down to 18mm. Then I turned down the top of the 1st topcap to 8mm appox.

I then extended the rod out a bit from the collet, and parted off leaving enough stock to be able to turn a spigot to fit the cylinder bore. Then I did the exact same again for the 2nd topcap. Then I remounted the topcaps in a 8mm collet ( gripping the freshly turned 8mm top of the topcaps ) to turn the spigot that would fit into the bore. I took off a fraction at a time, checking it against the cylinder bore, until it just fitted inside.

Then I got out my little jig mentioned earlier to drill the 4 holes in each of the topcaps. Then it was over to the cylinder block itself. Using the newly (re)made topcaps I marked out the positions for the mounting holes, drilled them and then tapped them M2 using my tapping stand.

Then it was just a case of building all the parts back up again. Funnily enough, the crosshead/rod-assembly that took all the fiddling the 1st time I built it up, took almost no fiddling this time to get moving. And wouldnt you know it, the one that went together easily last time, it took ages of fiddling and enlarging of the rod mounting holes ( I hadnt enlarged this set of holes the 1st time ) :bang:

But here is what the top looks like with the newly made topcaps.

Next it will be the bearing blocks. I am toying with the idea of using ball races in the bearing blocks, its only 4 ball races so the cost wouldnt be too bad.

Tim

spuddevans:
Got a little more done on this today.

I got started on making the bearing blocks. I took some square brass bar and chopped 4 pieces off it. I put the 4 bits in the vice on some parallels.

Now, I know that all 4 pieces came from the one bar, but I wanted to make sure that they each would be clamped tight so I put 4 little thin pieces of ali, one inbetween the moving jaw and each block. Then I tightened up the vice as tight as I could, and gently flycut the surfaces.

After a while I ended up with this,

Then I set up my very delicate and expensive vice stop, and after marking up the bearing blocks I set about center drilling and then drilling 4.8mm and then 5mm, all 4 blocks.

Resulting in this,

Now, getting impatient I carefully deburred the holes and whipped out a length of 5mm stainless rod and, aligning the blocks, I quickly shoved it through and immediately tried to turn it. Imagine my joy to find the rod spun freely....... But hang on, it spins a bit too freely :scratch:

And it kinda wobbles a bit too :scratch:

I immediately double checked the drill to make sure, yep it was 5mm. Then I checked the stainless rod with 1st calipers and then my digi micrometer,

:doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang: :doh: :bang:

My next move is to get some 5mm silver steel, and then check the bearing blocks. I guess I can make up the baseplate in the meantime. Oh well, just goes to show that you can't always trust 5mm stainless to actually BE 5mm.

Tim

Darren:
Hi Tim, you might also find the 5mm drill bit makes a bigger hole than 5mm..... :doh:

Reamers might be an idea here, they will be accurate. Also do you have one of those drill sets that go up in 0.1mm increments?
Not too expensive but real useful in this sort of situation...

spuddevans:

--- Quote from: Darren on August 18, 2009, 12:31:08 PM ---Hi Tim, you might also find the 5mm drill bit makes a bigger hole than 5mm..... :doh:

Reamers might be an idea here, they will be accurate. Also do you have one of those drill sets that go up in 0.1mm increments?
Not too expensive but real useful in this sort of situation...

--- End quote ---

Yea I do have 2 sets of drills that take me from 1.0mm-6mm and 6mm-10mm in 0.1mm stages, that's what I used on this. I 1st of all drilled the holes with a 4.8mm bit and then finished off with a 5mm bit.

I do have a 5mm reamer, so I can check to see if the hole itself is oversized, and if it is oversized I can fall back on my idea of using ball races, I have some 8mm OD 5mm ID bearings that would do quite nicely. I've also left the mill set up so that if I do need to bore out the holes for bearings I can just do it without zeroing in again.

The slight wiggle I felt was just that, slight. So I'm hoping that the holes are the right size and it is just the stainless rod that is undersize.

Tim

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