Here is a list of all the postings Martin Kyte has made in our forums. Click on a thread name to jump to the thread.
|Thread: To Pin or Not To Pin|
So not much harm done then. How was the crankshaft constructed?
So far I think the case for the use of pins in a loctite joint is not proven , at least to me. Couple of comments.
Yes keyways would be a lot stronger but we are talking about diametrical pins here.
Drilling for a pin reduces the area of adheasive contact and so reduces the strength of the bonded join in my example by about 5.5%.
You cannot possibly have equal load sharing unless either pre-stressed or the bonded joint can move, so were are still in the realm of the bond failing followed by the pin.
Personally I feel that the thinking may be somewhat historical. If in the past you were going to pin a crank and rely just on the pin 'gluing it all together with loctite holds the thing together whilst the pinning operation takes place. In this scenario we would be relying on the strength of the pin and any chemical bond is just a bonus. Early chemical bonds were really not as strong as current offerings and it takes time to build confidence in new techniques.( especially for us). Perhaps a s time went by the bonded joints became stronger with better the introduction of better products. and the pinning was done because that was what was always done. I don't know, but I'm interested in comments.
I do think the peace of mind statements are valid, just but for psychological reather than engineering reasons.
Finally how catastrophic is a joint failure on a miniture loco?
You are absolutely correct and of course I should have said web to shaft.
The point is why it's worth using glue and pin if indeed that is the case.
The question is about absolute failure modes really rather than what a loco would realistically produce. I'm really trying to acertain if there is any point at all in pinning as well as loctiting. The calcs (of which I am not best placed to do) should show if the pin is stronger or less strong than the loctite.
The crank pin dims were pulled out of the air as an example and as I said a 1/4 inch pin through the web is perhaps rather larger than would be typical.
The other side of the coin is the logical argument as expressed in my post.
At the moment I feel that there is no good argument for pinning if using loctite on the basis if the one fails then theother is going to as well.
The peace of mind argument is the same as Fred Dibnah banging in the ladder irons harder the higher he got. There was no point but he couldn't stop himself from doing it.
Hopefully someone will take the bait and do a proper analysis.
Edited By Martin Kyte on 10/09/2019 16:43:51
Reading some comments on pinning crankshafts on another thread and getting ready to complete a loco crankshaft raised the question do I or don't I pin the webs. Could someone with a brain more used to doing stress calcs than me solve this question once and for all and maybe find the fault in my logic too.
Scribblings gave me a value around 6630lb's force yeald strength for a 3/4 inch dia 3/4 inch crankpin in a 3/4 inch web. Assuming a 1/4 inch pin is used diametrically (rather a large size) I came up with 2000 lb shear strength or 4000lb for the double shear which is less than the failure point of the loctite joint. So if the loctite fails so will the pin.
If the loctite fails at a higher torque than the pin the pin must then fail too making the pin redundant. If the arrangement is that the pin fails at a higher torque then the loctite is redundant. And before you say that the pin and the loctite share the load that can only happen if there is movement which there cannot be. and assuming we haven't come up with some cunning plan to pre-stress the pin before hand.
The only conclusion I can come to is pin it or loctite it but not both.
PS loctite do encourage the use of chemical retainers with interference fits and I can see the point of that because it's clear that the bond and the shrink fit will both add to the strength of the joint.
Edited By Martin Kyte on 10/09/2019 14:12:47
|Thread: Are there any left?|
Well there was H Gee in Cambridge up untill a few weeks ago when Gee's burnt down. Appropriately due to an electrical fault.
I did visit about 6 years back for a cheap soldering iron and the shop was identical to how I remembered from my college days including the staff.
|Thread: Painting and Finishing|
Whilst I agree with the comment that Chris Vine's book is the bees knees (having read it) it would be good to have some less ambitious set up described as stepping stones along the way to Christophers professional standard set up. I would welcome such articles with great interest.
|Thread: What Did You Do Today 2019|
Bonhams are not exactly 'under the radar' so maybe the science museum is awake enough to notice.
I would have thought that the most significant piece was this one.
AN IMPORTANT 8 3/4-in GAUGE MODEL OF GEORGE STEPHENSON'S "NO. 1" 0-4-0 "LOCOMOTION", perported to have been constructed by George Stephenson and 'a friend',
It is certainly worth anybody's time to have a good look through the catalogue.
Yes Michael, I've just been scanning through the catalogue. We went down in 2006 ish when they were last going to sell everything off just to have a final look. I was so pleased that the entire collection had been bought and it looked as if, after restoration, it could be kept together rather than sold off piecemeal and sent to the 4 corners of the globe. It looks very much like this is now happening. I still have the original Bonhams catalogue for the entire collection and there were so many historic items particularly models by Stevenson and Timothy Hackworth to name a couple. Cartloads of original drawings on linen some of which were hand coloured. It's such a shame to see a collection broken up. I understand that the restoration of the site was far more expensive than originally envisaged and I guess with the financial crash coming on top of that it was a perfect storm.
It's amazing how some of these places managed to keep going for as long as they did really. I used to visit anytime I was in the area and several times I was the only person in the place. I don't know what the answer is really short of the goverment stepping in and saving things for the nation. Fat chance of that really, I don't think the current lot could run a bath.
Cannot agree with that.
For a start the consumer can buy a replacement power supply and just carry on using that. Apple only sell parts to registered apple repair centres which means that to repair/replace a mother board you are going to have to pay the cost of the new board plus the cost of the repair/replacement so even if the psu and the motherboard were the same price (which the are not) it would cost significantly more to replace the mother board.
Manufacture cost is but a small part of the price, a mother board contains significantly more electronics than a PSU and so is pricier in part alone. The bulk of the overhead is the R and D on both the hardware and software/firmware costs.
Personally I have never broken a Mac power connector and have been using Macs for ever.
|Thread: Black Oxide coating|
Does the colour make any odds to the corrosion resistance?
|Thread: What Did You Do Today 2019|
Merely that even if the connector breaks perhaps more than it should the primary design goal has still been achieved. So I aggree with you up to a point. It's still better to scrap the power adaptor than the computer.
I was responding to Nigels post primarily rather than you.
Edited By Martin Kyte on 12/08/2019 11:19:01
Is ensuring that the cheap bit (psu) breaks rather than the expensive bit (mother board) really bad design?
|Thread: Chuck out of true|
That's essentially what I said that the cylindrical register 'limits' the run out but even though you say your thread has a large clearance, it doesn't when it's tightened. Sounds like everything is nice and clean and concentric with you.
|Thread: Boiler testers and material verification|
No that isn't a silly question at all which is concerned with getting a boiler past the boiler inspectors.
When the thread heads for the realms of military and aerospace traceability I would say it is getting a little silly. Generally threads stay mostly around things that are practically helpful and I for one tend to pick up many usefull things from them. I was merely saying that the thread seemed to be getting a little fancifull.
It would be helpfull to know the answer to this but if you re making a boiler yourself maybe the better route would be to involve your club boiler inspector when you start and at strategic points along the way. That way you can ask if they are happy with the material/process/design mods etc as you go and will be in a position to act accordingly if something different is required. If I was a boiler inspector I'm sure I would be happier to work that way rather than be presented with a done deal.
As far as commercial boilers are concerned mine has a CE mark which shows it conforms.
Edited By Martin Kyte on 07/08/2019 16:25:03
Isn't this getting a little silly. The system in place works. Boilers are not blowing up all over the place and it's affordable. Traceability is not required. If one boiler goes pop the rest of the fleet will not have to be grounded so each boiler is treated seperately and you don't need to know what batch of material each bit came from. I would suspect that all boilers finally end their days either leaking beyond reasonable use or by failing their periodic pressure test. The fact that you are going to sit with the boiler pretty much between your legs is sufficient cause to generate a reasonable degree of caution. )
Ah you mean the materials certificate.
Go it now.
I suggest the bottom line is the only real test of safety factor is destructive testing (of each boiler), which somehow defeats the object.
The practical solutions is to do what is done now which is more an attempt to detect potentially dangerous boilers than certify absolute safety which cannot be done. If all the elements of the requirements are seen in the light of weeding out the duds it all makes better sense. The boilers that get through are then by implication safe for some given value of safe.
Don't quite understand CuP's point. Boiler certificates attests that the boiler inspector has done everything he is required to do and is happy. If CuP's response was to my post I don't expect it to mean anything else.
Perhaps I've missed something.
Surely the only claim can be to the insurance company and would be payed provided there were no acts of negligence which surely must include a valid and current boiler certificate.
Suing for damages needs to prove negligence on your part if down to the operation of the boiler or on the part of the boiler inspector if the boiler certificate was issued fraudulantly and the boiler were not fit for purpose.
I would hope that the inspector is legally responsable for ensuring that the boiler meets all the requirements. If not the certificate is not worth the paper it's written on which is fraud.
My commercial boiler certificate indicated the name third party independent assessors who validated the competence of the boiler tester.
Hopefully none of the above will come to pass if we all do our utmost to stick to the rules and operate as safely as we can.
|Thread: Dam Solution?|
The goyte is a fast running river, canals are designed for slow movement of water have a very small 'fall' except for locks wich have small byewiers to maintain levels are not designed for large volume discharge. The river has few constructions to be damaged and generally not much in the way of adjacent buildings. I have spent many an hour letting water down a canal lock flight in order to refill an empty pound that vandals had drained and it takes some deal of time when everything has to go through the gate paddles. The normal feeder for the canal will be small bore, little more than a drainage pipe. The video's I've seen have shown the discharge from the pumps flooding the bottom of the spillways which are adjacent to the reservoir. The spillways themselves are designed to discharge excess water direct into the local water course and are as such the intended way of dumping water.
Edited By Martin Kyte on 07/08/2019 09:40:30
|Thread: Boiler testers and material verification|
f I present some materials to a boiler inspector prior to building a boiler how does he verify that they are what my suppliers say they are ?
I if I was a boiler inspector 'which I'm not' what I would get from your presentation is that the materials appear to be copper or bronze and are the correct thicknesses for the design. In addition, and probably more usefully, it would show me that you appear to be an open and honest person who is interested in getting things right and working with me rather than trying to pull a fast one.
Steel boilers have more rigorous requirements regarding certification of materials, but I assume we are talking copper here.
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