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Post by fubar123 on Sept 30, 2021 7:58:46 GMT
I am just wondering if a wiper seal is available that small to help prevent the ingress of dust etc into the damper ?
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Post by Roger on Sept 30, 2021 8:15:29 GMT
I am just wondering if a wiper seal is available that small to help prevent the ingress of dust etc into the damper ? Possibly, but there needs to be an air hole to let it get in and out. However, I guess I could make a dust cover that could go over the outside. That could be a thin walled sleeve with a small hole for the shaft to go through.
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Post by steamer5 on Sept 30, 2021 8:22:00 GMT
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Post by Roger on Sept 30, 2021 8:39:04 GMT
Hi Kerrin, Possibly, but I was thinking more like they use on full sized dampers, it a thin shell that covers the outside of the body too. Something like this... Damper with dust cover by Georgia Montgomery, on Flickr
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Post by fubar123 on Sept 30, 2021 11:41:07 GMT
Only trying to help and not confuse Roger , according to ' Fluid Power ' catalogue they do a wiper ring ID down to 4mm with an OD of 9mm and a thickness of 5mm. Perhaps a bit to bulky for this application. Thinking out of the box , perhaps machine a sintered ball filter/seal to size fit and shape ? Chris
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Post by Roger on Sept 30, 2021 12:23:19 GMT
Only trying to help and not confuse Roger , according to ' Fluid Power ' catalogue they do a wiper ring ID down to 4mm with an OD of 9mm and a thickness of 5mm. Perhaps a bit to bulky for this application. Thinking out of the box , perhaps machine a sintered ball filter/seal to size fit and shape ? Chris Hi Chris. All contributions gratefully received. What isn't obvious from the model is that there's an air hole in the end cap which will suck air in and out as the piston moves, so sealing around the shaft isn't really going to help. That's why I've shown a cover which can be a close fit on the shaft and stay in position as the body moves. I think that's probably the most satisfactory solution to keeping the dust out.
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Post by andyhigham on Sept 30, 2021 15:04:44 GMT
A bit less complexity would be to make the damper like a motorcycle steering damper, with the rod passing all the way through the body. 20210930_155536 by Sigma Projects, on Flickr
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Post by Roger on Sept 30, 2021 15:21:01 GMT
A bit less complexity would be to make the damper like a motorcycle steering damper, with the rod passing all the way through the body. 20210930_155536 by Sigma Projects, on Flickr I was going to point you to my original design that I posted a few years ago which used this idea, but I couldn't find the page. However, it suffers from several issues. Firstly, it ends up being longer than the closed end design, and secondly, it makes attaching it more difficult. It also still required some way to keep it completely full of oil because any leakage will allow lost motion when it reverses. I don't know how that's done, maybe they have a floating piston which maintains the pressure. The only difference is that the piston wouldn't move during the action of the damper. I suspect that extra cylinder on the back of the main one has some function in that regard.
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Post by andyhigham on Sept 30, 2021 15:48:59 GMT
The chamber contains a pressurising system and the valves to allow for adjustability. This is a £400 damper, cheaper ones do not have the chamber. Older style suspension dampers had no bladder or floating piston, they had the rod uppermost and an air space above the piston so any slight leakage from the shaft seal was air not oil
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Post by Deleted on Sept 30, 2021 15:58:05 GMT
The chamber contains a pressurising system and the valves to allow for adjustability. This is a £400 damper, cheaper ones do not have the chamber. Older style suspension dampers had no bladder or floating piston, they had the rod uppermost and an air space above the piston so any slight leakage from the shaft seal was air not oil My old LWB series 2A land Rover had a steering damper, I fitted it as it was an option on later models. It was something that could save one from breaking a finger or even an arm when offroading with one wheel hitting a boulder. Pete
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Post by andyhigham on Sept 30, 2021 16:23:45 GMT
This is another type of damper I have fitted to my ZZR1400. It has a "pizza segment" shaped chamber with a rotary "piston" There is no volume change so no need for pressurisation. The actuating rod has a purely rotating motion so sealing is easier 20210930_171739 by Sigma Projects, on Flickr
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Post by Roger on Sept 30, 2021 17:31:06 GMT
The chamber contains a pressurising system and the valves to allow for adjustability. This is a £400 damper, cheaper ones do not have the chamber. Older style suspension dampers had no bladder or floating piston, they had the rod uppermost and an air space above the piston so any slight leakage from the shaft seal was air not oil My old LWB series 2A land Rover had a steering damper, I fitted it as it was an option on later models. It was something that could save one from breaking a finger or even an arm when offroading with one wheel hitting a boulder. Pete Hi Pete, I understand this is why they tell you to keep your thumbs away from the inside of the wheel so that you keep them attached.
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Post by Roger on Sept 30, 2021 17:35:18 GMT
This is another type of damper I have fitted to my ZZR1400. It has a "pizza segment" shaped chamber with a rotary "piston" There is no volume change so no need for pressurisation. The actuating rod has a purely rotating motion so sealing is easier 20210930_171739 by Sigma Projects, on Flickr I'd be curious to know how they deal with leakage or fill them initially. Any air or loss of volume is going to result in lost motion. Maybe the assumption is that they don't leak enough for that to be a problem. Another thing you have to handle in most shocks is cavitation. One of the videos showed that with a practical demonstration. If there's any rapid motion, I think they all need to be pressurised to prevent that happening. It might not need much, but you only need -15psi generated by the motion to create a vacuum.
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Post by andyhigham on Sept 30, 2021 18:22:44 GMT
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Post by Roger on Sept 30, 2021 21:43:55 GMT
In case you don't already have a good handle on Spring/Mass systems with damping, here's a neat simulation that shows one set of values. They provide a file that you can download if you have MATLAB at your disposal. The key takeaways are these... 1) The adjustable response can be very different depending on how much damping you have. 2) The response ulitmately settles on a clear final value. If you have leaf springs, you can't alter the amount of damping, and it won't settle on a clear final value. The more friction you have, the further it can settle from equilibrium. Anyway, these are the facts, I'll let the results speak for themselves. This is how we move Model Engineering out of the Dark Ages. This is the setup for machining the spanner flats on the Piston rod. I'm starting to cash in on the efforts made to automate the indexing of the 4th axis. All I had to do as add the text ANGLEREP2 to the operation and expand it with a click of a button when exporting it. That automatically generates a program that runs the program twice, once at zero degrees and again at 180 degrees. 20210930_121212 by Georgia Montgomery, on Flickr The flat is 3mm wide and 0.5mm deep, so it's done in two cuts with a 3mm cutter. It's Silver Steel with a long overhang on the cutter, so it's best to take it gently. 20210930_121202 by Georgia Montgomery, on Flickr Here's a video showing the 4th axis in action. 20210930_121305 by Georgia Montgomery, on Flickr The rod end pivot is 6mm Silver Steel which has an M4 x 0.5 (fine) thread 20210930_124432 by Georgia Montgomery, on Flickr It's surprising how compact this is compared to commercial units for RC cars. I only need 9.5mm total travel. 20210930_143705 by Georgia Montgomery, on Flickr The free piston is dead easy to make from Brass. The 8mm clearance pocket was made by plunging an 8mm milling cutter into the right depth on the Lathe after drilling the tapping size. It's easier to do this when the centre has been remover. I've gone for an initial 15% compression on the O-rings, but that might end up slightly less. I'll see how freely it moves as an assembly. 20210930_151029 by Georgia Montgomery, on Flickr This is a scrap of thin Copper sheet being made into a washer. I didn't have an M2 standard mandrel, so I made that first. 20210930_154523 by Georgia Montgomery, on Flickr This tool is ideal for this kind of work. 20210930_154740 by Georgia Montgomery, on Flickr The Cap Screw is M2 so that the head diameter is smaller than the ID of the Belleville washers. 20210930_155749 by Georgia Montgomery, on Flickr This is just a bleed hole. 20210930_155933 by Georgia Montgomery, on Flickr Hopefully the M14 x 0.75 (fine) tap won't be too long coming. I can't make the cylinder and top cap until that comes because I need to create the Female thread first then match the one on the body to that. It's all pretty easy to make, and won't take long once the tap arrives.
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Post by Roger on Oct 1, 2021 9:23:49 GMT
Ok, that looks like they don't expect any leakage, it's just filled and sealed once the air has been bled out. I guess there won't be a problem until it's been in service for a long time.
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Post by Roger on Oct 1, 2021 11:49:57 GMT
This is the top Fork Mount for the Damper. The outside was machined with an 8mm cutter, this is the 4mm one used for the slot. 20210930_231559 by Georgia Montgomery, on Flickr Once the Wobbler had found the end and middle, the tool was set by touching down on the top face of the flat. I measured the thickness there, halved it and put that in as the Z-axis DRO. That makes the centre of the bar zero which is what I need to turn it over and machine it from both sides. 20211001_101729 by Georgia Montgomery, on Flickr 20211001_105318 by Georgia Montgomery, on Flickr The is the frame mount that will take the forked pivot above. This was machined with a 10mm Carbide 2-flute 20211001_123130 by Georgia Montgomery, on Flickr
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Post by Roger on Oct 1, 2021 21:27:16 GMT
A bit more progress on the damper today, this is going to be the bottom Yolk that attaches to the bearing on the axle. It's being roughed out with a knackered 10mm Carbide 2-flute cutter, but it's good enough for this job even though it's clearly not happy. 20211001_215725 by Georgia Montgomery, on Flickr That's all finished off with a 4-flute HSS End Mill which isn't centre cutting. I was given this by a customer who salvaged the cutters when they disbanded the machine shop. Normally these aren't any good for CNC work, but since I'm just finishing on the sides, it's fine. 20211001_222106 by Georgia Montgomery, on Flickr
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Post by Roger on Oct 2, 2021 20:36:26 GMT
Now that the M14 x 0.75 (fine) tap had arrived, I could get on with making the Top Cap and Body. The Top Cap is made from SAE660 so it's very easy to machine. I drilled through first and then used a 12mm Slot Drill to rough it out to depth before finishing off with a boring bar. 20211002_152451 by Georgia Montgomery, on Flickr 20211002_154223 by Georgia Montgomery, on Flickr This is the Body with the mating thread, ready for Screw Cutting. 20211002_163819 by Georgia Montgomery, on Flickr 20211002_204311 by Georgia Montgomery, on Flickr 20211002_204253 by Georgia Montgomery, on Flickr The bore was then roughed out in the same manner, this time using an 8mm then 10mm End Mill before boring to size. The floating piston is a nice close fit. 20211002_212155 by Georgia Montgomery, on Flickr I'll leave the Body on the stock for the time being, it's easier to add the spanner flats while I can hold it on the stock. The Cap can be parted off because I need to get to the other end to add the lug details. I scrapped the bottom attachment piece I was making yesterday because I decided that the end bearings were on the thin side. The gap has been reduced to 18mm from 20mm and I'm currently machining the new one. That's taken longer than expected because Bill Gates thinks it's ok to restart the PC whenever he feels like it to install updates! Fortunately, this new controller allows me to use the reference marks on the Linear Scales, so I just homed the machine and started it off again with just a sanity check to see if it was plausibly in the right place. That worked fine, so I know I can trust it.
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Post by Roger on Oct 3, 2021 21:42:56 GMT
The curved ends and the two holes were added, turning the 4th axis through 90 degrees to get to them from each side. 20211003_151410 by Georgia Montgomery, on Flickr That was tidied up with a file and the slot and rear shape added. 20211003_213506 by Georgia Montgomery, on Flickr This had to be done fairly gently since I can't really get hold of this. It needs to stand clear of the vice to give the cutter clearance at the ends where it drops off the radius. 20211003_222210 by Georgia Montgomery, on Flickr With that out of the way, the spanned flats on the body finally got done. I should have found a sharper cutter! 20211003_152946 by Georgia Montgomery, on Flickr The body is pretty thin, and I needed to screw cut the thread on the closed end. That meant making another of those support pieces for the back of the collet. There's far too great a chance of damaging the part in the 3-jaw, it's just not possible to hold it firmly enough without distorting it. I haven't shown it here, but I slid the free piston inside the end for extra support. 20211003_164249 by Georgia Montgomery, on Flickr This end has the hole for the Piston Rod and also the two O-rings. I decided to put the rod hole in from this end rather than from the other. I thought I'd get it more central if I did it that way. The thread was screw cut with less aggressive cuts than usual to make sure nothing moved. 20211003_215507 by Georgia Montgomery, on Flickr The end cap fits nicely, so that's good. 20211003_215450 by Georgia Montgomery, on Flickr It's gradually coming together, most of the cylinder parts are finished with the exception of the fixing lug on the Top Cap. 20211003_222413 by Georgia Montgomery, on Flickr The mounts are almost finished, but the pins still need to be made. Then I will have to dismantle the Anti-Roll bar and machine that to suit the cylinder mount. Once this has all been proven, the others won't take long to make.
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