Gallery, Projects and General > Gallery
What do you do when you're given some 1.25" aluminium Hex bar
SwarfnStuff:
Hi Joules,
I do like looking at what you are doing and reckon it is a real challenge to get 6 con-rods and crank playing nicely together. Specially as you are designing on the fly.
Heck, I'm currently struggling with a single cylinder model that even after boring and taking several spring passes is still tight at the inner (Blind) end of said cylinder let alone six of em.
Keeps me amused during this virus enforced stay home or else problem.
John B
Joules:
Ahh, you see John that’s the advantage of never having designed or built anything like this. You don’t know the limitations till you hit them. It will probably be that each cylinder will need numbering and have a matching piston. I am leaving wiggle room in the design for parts to find there own positions, that too could translate to vibration and rapid wear of parts. I am enjoying the challenge of machining the parts as it is demanding at this level.
Good luck with your build.
Joules:
You know when you make an "EPIC" spacer, a career defining spacer and drop it !!!
Well this wasn't it, but I did drop it... :bang: However on this occasion I found it round the back of the lathe.
I made a start, for want of a better word, on my con rod spider. I went with brass as the con rods are going to be brass so they stand a better chance with the gudgeon pins. The stock for the spider was machined to size, drilled and reamed before turning and parting off each half. It was then back over to the mill for more DRO bolt circle drilling. I used the square ER32 collet block again, the picture below shows the split bush used to pull the block down to the table. I then spent a happy 45 minutes trying to get the now back to back, spider halves level. I had made a Delrin stand off to support the discs in the collet, I should probably have made a mandrel to support them, and then bolted them to it. As it was a one time job I thought I could bodge it, only the 1mm holes are critical. That was just as well, as when I drilled the 2.8mm holes the top disc pulled out the collet and was spinning on the drill bit !!! First hole, luckily I was able to slide the disc back into the collet using the drill as a guide and nip the nut up a little more, that will have thrown my carefully got centre. These are just holes for lightening the spider, unlike the 1mm holes which will be locators for the gudgeon pins, they are clamped between the two halves.
I have a couple of used flanged bearings left over from model helicopter flying (loose term) The spacer seats the bearing outer and acts as a guide to keep the spider concentric. The last image gives you some scale to the spider when fitted in the crankcase. At this point I have pretty much caught up on my CAD progress so far. I am looking into making the gudgeon pins, be they turned or ground on the ends. Another jig to make for machining the con rods, and the fun job of making and securing the fixed rod that guides the spider round. Like eating an elephant, one bite at a time.
SwarfnStuff:
Pretty sure Rolls-Royce were individual cylinders and matching pistons - before mass production.
Plus a chap here in OZ made a Model Tiger tank and if memory serves me they had 12 cylinders, all of his were made with matching pistons so you are in good company.
John B
Joules:
My M2 bolts arrived, I can finally bolt on the cylinders and take some measurements. You may recall way back, the crankcase was the project. It meant I didn't apply the same precision to it I have applied to later parts. Here is where I find my errors and the play in my setup. The crankcase was drilled though in three hits, so the opposing cylinder pairs should be inline. The bolt holes for the cylinders had to be drilled and tapped per cylinder, and this is where errors crept in that I thought I would be able to ignore, cause I'm never going to build this !!!
All bar one bolt circle on the crankcase was within tolerance. The out of tolerance bolt circle needed some needle file work on the cylinder mounting holes. All the cylinders have one orientation, I can't turn them 180 degree, so something was amiss in my hole drilling to cylinder centre. Each cylinder has had to be marked and corresponding marks within the crankcase define position and direction when the parts need disassembling. I then checked cylinder pair alignment using the 6.5mm drill used on the cylinders. I am good to a thou or so inline, the cylinder with the out of tolerance bolt circle had the most drag. The cylinders will be bored out to 7mm and the intention is to do them on the crankcase in pairs, that way I can correct the worst case pair out by 0.003" That is well within my 0.010" tolerance on the spider, however the closer I get it, other cumulative errors aren't going to nudge me out of tolerance.
Not a lot to show for today other than screwing it together and learning how much the mill can flex and bend at the tool. Basically, everything I set out to learn and figure how to work round the limitations.
John, I had the pleasure a couple of years ago of getting some hands on with a stripped down vintage Rolls engine. It was a fantastic experience and I learned a lot about the workmanship of that time, a once in a lifetime opportunity.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version