Another Paddleducks build log

[spuddevans]

Not too much to report on today, I've only had a little time in the workshop and spent most of it just standing there wondering 

The bit that has got me wondering is the Block mounting plate



I was going to PM Bogs to ask him this, but I figured I may not be the only one who, when building this, has not got the exact materials that I thought I had, so I thought if the answer could be put into the main build log then anyone could find out.

As you can see on the plans it calls for 2-2.5mm brass or steel sheet and I thought I had some 2mm brass sheet, but it turns out after measuring a part that didnt have a beaten edge (note to self, always check to make sure when using verniers to make sure the jaws lie flat and square to the bit being measured) it is only 1.62mm (1/16") thick. Now I have got some 2.5mm ali' plate that is big enough, but before hacking my way into that I wanted to know if (1) would the 1.62mm brass be too weak/thin? and (2) if that is the case, would the ali do instead?

So If anyone has an answer please chime in and I will be eternally grateful 


Tim

[kvom]

Bogs' drawing suggests not going any thinner, whether for rigidity or dimensionality I can't say.  I made my plates from 1/4" brass that was flycut a few thousands on each side. 

Note that when the plate is thinner, the piston will be higher in the cylinder at TDC, as will the valves.  You might need to do some calculations to see if that causes a problem.  You will have the weight of the block plus the steam chests supported by the four columns on the edges.  If the plate is able to flex from the weight or vibrations then binding could occur.

In short, I'd probably use the Al plate myself.

[spuddevans]

.......In short, I'd probably use the Al plate myself.

That is what I am expecting to do, I guess I'm just vainly hoping that the brass would do. But like you say about the weight and vibrations, it'll probably be better to err on the side of caution.

Thanks Kvom 


Tim

[bogstandard]

Tim,

Kirk has it almost spot on. 1/16th is really a little too thin to support the weight of the whole top end, and the friction induced forces going up and down. Brass or steel was chosen for it's rigidity. Steel because it is rigid from the off, and brass after it has worked hardened, will be strong enough to do the job. I am not too sure that the ali, with it's natural softness, would be up to the job, you would have to suck it and see. 3mm ali would be much better.

If it was flat enough, you could use two layers of the brass plate, say loctited together (not soldered, that would soften the material too much). The amount of bolts holding things together on the top end would ensure it acted like a single thickness.

You will hit the same problem when the bottom plate is made. So your choice has to be made at this time.

By going thicker, the only things that really have to be taken in consideration are the bolt lengths and the four column lengths. The bolts would need to be longer than the difference in thickness from 2mm, and the columns, shorter.


John

[spuddevans]

Thanks John, I think I'll pick up some 2mm brass for both the top and bottom plates, I think that will be the best solution all round.

I think I was grasping at straws once I found out the brass was thinner than I thought.

Oh well, I live and learn a bit more.

Til I get my brass sheet there's a few other things I can be getting on with until I get it.


Thanks again for helping me 


Tim

[shred]

FWIW, mine's plates are 3mm Ali (~1/8"), and works well, but I don't think much thinner would be a good idea.

[bogstandard]

There you go Tim, straight from a man who has had the experience of doing it.


Bogs

[spuddevans]

Thanks Shred, if I had some 3mm ali I would use that , but my ali is only 2.5mm and I dont want to risk it. I'll wait until I get some 2mm brass sheet.

There you go Tim, straight from a man who has had the experience of doing it.

That's what I love about this forum, there is always someone who has already done either the exact same thing or a similar thing who can share their experience with those like me who are still relatively new to machining,   



Thanks guys 
Tim

[spuddevans]

Well I got just a little more done this afternoon.

I marked up the main block for the steam ports, and realising that they are centrally aligned and are set in the same distance from the end I decided to use my very high-tech vice stop to make drilling a lot easier. ( hey, I'm really getting into this whole "using jigs and stops to make machining easier" thing!  ) 1st up was center drilling the 4 ports, then drilling through to the cylinder bores.



Then, not yet having in my grubby little hands the 2mm brass sheet needed for the mounting plates, I skipped on a couple of steps in the plans to make some of the little things. I made the 4 crosshead rods, well, when I say I made them I just cut some 4mm stainless rod to length and then drilled and tapped one end.

Then I marked up the piston+rod assembly for cutting to length, chucked up a piston with the rod facing out of the ER32 collet and parted off to size, then did the same to the other piston assembly. Then I single pointed a M3 thread on each piston rod and finished off the thread with a M3 die.

So here is a mockup of the crosshead rods in the crossheads, along with the threaded piston assemblies also mounted in the crossheads.



That's all for today, stay tuned for more of the same different.

Tim

[CrewCab]

Nicely done Tim, I must say I'm impressed how you've mastered the "dark art of single point threading"    ........... the threads on the small SS rods looks very professional  .............. before my self imposed exile from the workshop around last Christmas  I was trying to get the hang using a bit of delrin, I must get back to that 

Thanks for the continued updates, nice to see your progress.

CC

[bogstandard]

Tim,

As you gain experience, you will find yourself knocking up little jigs and fixtures to allow you to save loads of time and effort, and obtain that elusive accuracy between parts.

The mill backstop is an essential part of machining, and as you have shown, there is no need for it to be fancy, as long as it does the job.

Nice one.

Bogs

[spuddevans]

Nicely done Tim, I must say I'm impressed how you've mastered the "dark art of single point threading"    ........... the threads on the small SS rods looks very professional  .............. before my self imposed exile from the workshop around last Christmas  I was trying to get the hang using a bit of delrin, I must get back to that 

Well thank you good sir, but before my head swells beyond belief, I should tell you that those threads were cleaned up by running a M3 die over them, I didnt go to full depth single pointing. I also spent about half an hour hunting in vain for my newly ground up threading tool which seems to have evolved legs and the ability to deliberately hide from me   Still havent found it, it'll probably turn up about 2.5mins after I grind up a new one.

The mill backstop is an essential part of machining, and as you have shown, there is no need for it to be fancy, as long as it does the job.

Making a mill backstop is right underneath the tailstock die holder on the "to-do" list  til then I make use of a spare hold-down clamp.

Thanks for following guys,
Tim

[Darren]

Thanks for following guys,
Tim

Thanks for showing.....that quick backstop was good thinking to keep the flow.....

[CrewCab]

I should tell you that those threads were cleaned up by running a M3 die over them, I didnt go to full depth single pointing. 

Nothing wrong with that imho, single pointing gets the thread square to the material, finishing off with a die just gets you to the correct depth quicker  ................. see ................ I know the theory 

I also spent about half an hour hunting in vain for my newly ground up threading tool which seems to have evolved legs and the ability to deliberately hide from me  Still haven't found it, it'll probably turn up about 2.5mins after I grind up a new one.

A'int that always the way 

Keep the faith 

CC

[spuddevans]

Well I made a little progress today (the emphasis being on "little")  I got some 2mm brass sheet and hacked off a section and then milled the 2 freshly cut edges smooth and to size. I then blued ( well, blacked actually ) one surface with layout dye ( a big black marker from tescos ) and then spent a fair bit of time marking out all the holes, remembering that I had to make an adjustment for one set of crosshead-rod-mounting-holes as I had drilled one crosshead slightly incorrectly.




Just after taking that Pic I removed the piece from the vice and just made little centre punch marks ( more like "pop" marks actually ), then remounted it in the vice and drilled all the small holes. For the 2 packing gland holes I drilled out as big as I had drills ( 13mm ) and then switched to my Boring bar setup. While not ideal for this, it seemed to work ok, although a little slow. ( My boring bar is marked in imperial and I was working in metric, so progress was a little slow as I approached final diameter as I didnt want to over-shoot if I could help it )

Here's the top-plate bored out, sitting on the main cylinder block and the packing glands sitting in place.



Next I have to drill and tap for the packing gland / top-cap mounting holes, and drill and tap for the mounting plate holes.


Tim

[sbwhart]

Coming along nicely Tim 

Stew

[kvom]

Just a reminder that the cutouts on the side of the top plate are not optional, as you need clearance for the steam chests.  The cutouts in the front and back are optional.

[spuddevans]

Just a reminder that the cutouts on the side of the top plate are not optional, as you need clearance for the steam chests.  The cutouts in the front and back are optional.

Thanks for that Kvom, I hadn't realised that.  That will be next on the list to do then.


Tim

[kvom]

On mine the flange of the steam chest packing gland is a little bit wider than the width of the steam chest, so I had to cut the sides a tad deaper than the edge of the block. 

[spuddevans]

Got a bit more done today, I started by milling out a recess on the mounting plate for the steam chests.

Then I drilled and tapped the cylinder block using a newly aquired tapping stand, I totally reccomend everyone either make or buy one, makes tapping so much easier 

I only drilled and tapped the bottom of the block as I've decided to remake the top-caps as I messed up the holes on them.

I then did a little assembly. After a little polishing on one piston, ( on the rod not the actual piston, as the rod was slightly oversize ( about 0.04mm ) and would not go through the packing gland ) I was able to assemble the pistons and packing glands into the cylinder, and then attach the mounting plate.

Then I assembled the crossheads and rods, and after a little fiddling and messing around, widening one set of crosshead-rod-holes a little, and ...... It slides in and out !!! (ok a little stiff, but it still works)








So next I'll be working on making 2 new top-caps, then it'll be on to the bearing blocks.


Tim

[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 ) 

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 

And it kinda wobbles a bit too 

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,



 



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.....

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]

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

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...

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