Designing & making main U/C with springs, dampers and brakes
9463 forum posts
Still reading the excellent blog.....keep going. I know it takes effort and time to write and publish these, your skills are stunning
|alan p||23/10/2020 08:57:45|
|323 forum posts|
Good to see you back Ken.
Given the 115mm spindle length as a guide you have supple digits to assemble those. A great example of micro engineering and lateral thinking. Like using the spring section as a clip, must keep that one in mind
|354 forum posts|
Super interesting Ken Not an engineer nor ever will be but absolutely fascinated by the skill and ingenuity, so genuinely interested to see it to a conclusion.
|kenking-King Design||17/11/2020 00:48:09|
301 forum posts
Back again after a week of tummy trouble, which at least served to take my mind off two separate ear infections (one each side). Combined, these events hampered progress more than somewhat. Apologies if you find that too much information.
I meant to say in my last posting that as the project is now being interest-only driven it will inevitably sometimes take a back seat, and that I will from now on only issue a new post when there has been significant progress, with a reasonable amount of stuff to show you. This post maybe doesn't completely satisfy that brief, but hereafter I'll stick to it, so there may be barren periods to get through, particularly with Christmas approaching.
After some consideration a design change was made to the belly bands. I decided to make them of brass and to solder them in place, rather than using the aluminium ones and trying to bond them in a precise position whilst sliding them along the cylinder. In the light of later experience that turned out to be a good decision. Belly bands locate the damper cylinders correctly within the legs, so position is important ....
After that the filling and vent ports in the lower damper endcaps were drilled, and tapped 10 BA, holes angled as my earlier sketch suggested. I ground down the OD of a small centre drill and used it to provide a conical seat ......
with 10BA steel cheesehead screws as plugs, bedding down onto them. They are VERY SMALL !
Because they sit within the lower leg tube I had to make the heads slightly conical so that they did not extend out past the endcap diameter to foul the tube bore.
For assembly of the damper cylinders I bought the recommended Loctite 603 and 7603 Cleaner and thought I would bond in the UPPER endcaps first, following the suggested procedure after cleaning, firstly wetting a 3mm band inside the brass cylinder, then the mating land of the endcap, bringing them together with a twisting motion.
HAH, I wish ! No sooner had the two parts caught sight of each other than they were STUCK, really STUCK. No chance of full engagement nor alignment. To illustate that I'm a slow learner I can tell you I tried three assemblies before deciding something had to change ( once I'd used carefully applied heat to dissassemble three failures, that is). After carefully rereading instructions from Loctite, plus the Product Data Sheet, I realised I was woefully short of the recomended diametral clearance of 0.1mm, having proudly made things a nice sliding fit.
Glossing over the sordid details, including turning a few thou off each encap, I tried again with SUCCESS !! Boy, that is some adhesive. 'O'rings were fitted to all eight endcaps, and the next steps considered. Final assembly required pistons to be affixed to spindles, and the spindles to be inserted into the cylinders and through upper caps. A LOWER encap would then be slid a little way onto the spindle before very careful application of 603 as before, followed by a short prayer and rapid insertion into the cylinder tube.
OK, procedure established, but before following it I had to modify the pistons slightly by relieving part of the OD to reduce occasional binding noticed during dry runs. That done it was time to bite the bullet, and thankfully all went well. Endcaps went fully home and I avoided glueing any pistons to bores .... PHEW !!
Having allowed some hours for full adhesive cure, as suggested, it was time to fill with oil. My wife shares the typical femal abhorrence of any fluid such as engine oil being introduced into the domestic environment so I was denied the comfort of the living room, but proceeded to plan. First lesson -- don't bother trying to fill the syringe by sucking up through the needle, unless you have all day. Second lesson -- having successfully filled said syringe, it's awfully hard work to pump it into the cylinder. Shortening the needle will help enormously !
Here you see needle, cylinder, and two of those VERY SMALL screwpugs I mentioned ....
and here is a completed cylinder awaiting assembly to its spring and springcap prior to insertion into a leg ....
Piston action is smooth, little resistance to movement in one direction but quite noticeable in the other showing that the piston valve really works. Relieving part of the piston OD has definitely reduced the damping effect, by shortening the restricted path length for the oil passing the piston rim. Substituting a more viscous oil may be something to consider after more trials, so still some work to be done, but I'm encouraged by what has been achieved, and VERY pleased to have those tiny fiddly bits behind me.
More at some future date, and a Merry Christmas to you all,
9463 forum posts
Excellent and interesting as always. Great to hear ( no pun intended) you’re on the mend
|alan p||17/11/2020 08:02:38|
|323 forum posts|
Welcome back Ken.
O.1 mm does give the impression of a chasm after fine tolerances . Good to see a satisfactory result.
Watching brief for any future updates.
Wishing you a good recovery from your aliments, a Merry Christmas and hopefully a more enjoyable 2021.
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