|
Post by tdaharvey on Sept 21, 2020 20:51:17 GMT
Hi I am repairing an LBSC 3.5 Britannia frame which has been dropped at some point causing misalignment. Having stripped it down and repaired the damage I am now working on reassembly. I am thinking about using loctite on the stretchers to ensure they don't move again but would probably use loctite 638 rather than 271 which is for permanent application - just in case I need to take the frames apart again. Does this make sense? Any advice? Trevor
|
|
|
Post by delaplume on Sept 21, 2020 21:09:05 GMT
Hello Trevor,
You say}---" using loctite on the stretchers to ensure they don't move again ".........Why did they move in the first place ??..........I don't have a set of drawings for the small Brit. bit if designed along conventional lines the stretchers are usually secured to the mainframes by countersunk screws...5BA maybe ??..........Do you want to do away with the screws and use only Loctite to bond the frames to the stretchers ??.....or do you want to Loctite the screws in place ??
Personally I'd stay with convention and let someone else do the R & D on this one.......Yes, secure the screws with Loctite by all means....
Don't forget that Loctite can be overcome using heat.....like a small propane torch from B&Q etc....
Just a thought}---- Have you looked into having a set of frames lase cut ??......Might be cheaper than you think...
Alan
|
|
|
Post by ettingtonliam on Sept 21, 2020 22:48:40 GMT
Loctite isn't really an adhesive is it? I don't quite see how it would help to stop your frame stretchers from moving, other than stopping the bolts from working loose.
As Alan says, the usual thing is multiple csk screws, but if you didn't want to rely on the csk heads from stopping sliding movement in the joint, why not add a couple of dowels on each side?
|
|
uuu
Elder Statesman
your message here...
Posts: 2,800
|
Post by uuu on Sept 22, 2020 7:07:29 GMT
A bit of Loctite won't hurt at all. Go for it. If you start down the road of altering things, you'll get sucked in and spend years at it.
Wilf
|
|
|
Post by ettingtonliam on Sept 22, 2020 9:46:03 GMT
No, it won't hurt, but apart from stopping the screws/bolts coming out, I'm not sure I see what good it will do either.
|
|
|
Post by Deleted on Sept 22, 2020 10:08:00 GMT
My own frames are assembled using a Loctite thread lock to stop the screws from coming loose in operation and I even have some small sections where steel has been bonded onto the frames to fill some slots using Loctite 638 alone. However, if you are thinking of using 'Loctite' alone to effectively 'glue' the stretchers on with no mechanical means of securing them, then 'no, I wouldn't think this a good idea?
Pete
|
|
|
Post by RGR 60130 on Sept 22, 2020 11:46:29 GMT
Trevor,
In your post you said that the cause of the misalignment was the loco being dropped. In that case wouldn't the remedy be to not drop it again? Funnily enough I had one which had suffered the same fate. After loosening all the stretcher screws it came straight again. I can't see Loctiting things achieving anything and it may well cause problems when you want to do maintenance in the future.
Reg
|
|
44767
Statesman
Posts: 529
|
Post by 44767 on Sept 22, 2020 12:08:56 GMT
My take on fastenings is that it is the friction from the clamping force when the screws are tightened or the rivets are closed that holds parts in place and stops them from moving. Screws and bolts should not be used to locate parts; this should be done by locating against shoulders or, as was mentioned earlier, by the use of dowels. Screws should pass through clearance holes. Using Loctite on the screw does not change this clamping force which is only achieved by torquing the screw to the prescribed value.
There are Loctite products which are adhesives and could be added between mating surfaces but they still require the parts to be clamped while they set and they do have a thickness which needs to be accounted for to be sure the assembly stays accurate.
Mike
|
|
|
Post by tdaharvey on Sept 22, 2020 19:58:24 GMT
Guys thanks for all your comments - really helpful.
So just to confirm that this chassis appears to have been dropped in the past on one side of the draw bar and this shock has transferred through the frames resulting in distortion and the axles being off square. I have completely stripped the frames back to basics straightened them and some other damage I fougnd. The stretchers are riveted to right angles sections which are secured to the frames using 7 ba counter sunk screws, There are no dowels to locate the stretchers so there is forward and backwards movement that is helping to restore the frame alignments and axle positions. I think though that the stretchers may no longer be square as I am not quite getting things completely straight - I will straighten these or make new ones.
So why was I thinking about loctite? Simply that once I get everything straight I was thinking that I need something more than countersunk screws to keep it square - I am thinking that there is a lot of racking force on the frames and so movement is possible. I like the idea of dowels to keep things in place and will pop a few in when I have everything straightened amd bolted together.
Thanks again for your assistance. Regards Trevor
|
|
|
Post by daveburrage on Sept 24, 2020 15:43:14 GMT
The idea of using loctite between the mating faces is perfectly valid and it improves the structural integrity. Bolted faces like stretchers usually fail by "shuffling" between the faces if there is insufficient bolt clamping force. Although loctite does not increase the clamp force it does increase the friction co-eff between the plates and it is this that reduces the likelyhood of "shuffling". Shotblasting has a similar effect, there are also various high friction shims that can be fitted between the 2 plates.
Another possibility is to use very high tensile cap screws. If tightened to the recommended torque they will increase the clamp force - again giving a more secure joint.
regards
Dave Burrage (Structures engineer in a previous life)
|
|
|
Post by ettingtonliam on Sept 24, 2020 19:15:31 GMT
Stretchers consisting of a vertical plate attached to angles, which run from one frame plate to the other don't have a lot of resistance to the frames 'working' under alternating piston thrusts. Any chance you can work in a substantial horizontal stretcher? That will improve frame stiffness considerably.
|
|
|
Post by suctionhose on Sept 25, 2020 5:55:12 GMT
Components that "square up" the frames are: smokebox saddles, drag box in the rear, inside cylinders or horizontal stretchers which are some times there.
Problem is each of these items are disconnected from each other so the flat frames flap around in between like a parallelogram.
The frame needs continuous longitudinal support which comes from the running boards or the side tanks on many traditional designs.
In later days, while the Americans swore by the cast bed, the British Standard locos persevered with plate frames. I think running boards of say, a Britannia or 9f, hung off the boiler then? I don't know how the frames stayed straight after that
|
|
mbrown
Elder Statesman
Posts: 1,713
|
Post by mbrown on Sept 25, 2020 7:34:00 GMT
There are some interesting reflections on frame stiffness in Eric Langridge's book "Under 10 CMEs". He notes that Urie's LSWR locos had very robust running boards and valances which contributed to frame stiffness, and it is clear that he agrees that cutting down on the rigidity of these parts was a worrying move.
On the other hand, the BR Standards had very extensive horizontal and vertical staying between the frames - one reason Riddles stuck firmly to two outside cylinders except (reluctantly, I believe) on the Duke.
Maybe two ways to approach the same problem...
Malcolm
|
|
uuu
Elder Statesman
your message here...
Posts: 2,800
|
Post by uuu on Sept 25, 2020 8:54:49 GMT
Welding is an option, of course (back to thinking about models).
Wilf
|
|
|
Post by delaplume on Sept 25, 2020 10:34:49 GMT
Welding is an option, of course (back to thinking about models). Wilf In the past I've Brased the bufferbeam / mainframe and dragbeam / mainframe but only after clamping heavy duty spacers between the plate frames to avoid distortion....... Instead of Loctite you might consider soft solder "tinned" and wiped onto both flat faces then after assembly run the flame over the joint to finally "Sweat" it into one piece...... ( Cheaper than Loctite and more durable I'd say..) Regarding the horizontal stretcher}---- Martin Evans 5"g Simplex has a very heavy duty one just aft of the saddle / cylinders assembly... During my time at Bridgnorth I know that the full-size locos made good use of Fitted Bolts for alignment.....Admittedly this was on Ex-GWR and LMS locos in the main.... Just a passing thought but the SR's 0-6-0 Q1 "Coffee Pot" didn't have any running boards--- did it ??
|
|
oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 688
|
Post by oldnorton on Sept 25, 2020 17:04:41 GMT
Components that "square up" the frames are: smokebox saddles, drag box in the rear, inside cylinders or horizontal stretchers which are some times there. Problem is each of these items are disconnected from each other so the flat frames flap around in between like a parallelogram. The frame needs continuous longitudinal support which comes from the running boards or the side tanks on many traditional designs. In later days, while the Americans swore by the cast bed, the British Standard locos persevered with plate frames. I think running boards of say, a Britannia or 9f, hung off the boiler then? I don't know how the frames stayed straight after that Ross Totally agree with you that the frames need stretchers designed to resist the racking forces. Not sure that the Running PLATES or Side Platforms were ever designed for that purpose (more for holding up a walking person and the odd lubricator!). The Britannia had a large central horizontal stretcher for resisting these forces. Norm
|
|
|
Post by suctionhose on Sept 26, 2020 0:58:57 GMT
As evidence in support of my claims of the structural function of running boards and tanks, I submit the following: The first is my model of a Beyer Peacock 2-8-0 (Our NSWGR Standard Goods): Even with a box at the front end comprising a horizontal stretcher extending back from the front buffer beam to form the floor of the smokebox and beyond intersecting with a full depth "motion plate" and another horizontal stretcher at the bottom of the frame under the steam chests, this frame was a floppy as a piece cardboard until the running boards went on. Especially in the area were the firebox sat in spite of a solid stretcher in front of the f/box and the drag box taking all the space behind the f/box (under the footplate) The second is my model of this 2ft gauge 0-6-2. the frame plates are 8mm thick steel with stretchers as per original. Once again, surprisingly floppy until the footplate was screwed down. I departed for prototype by replacing a massive smokebox saddle casting containing steam and exhaust pipes with a light fabrication (less thermal mass). I fitted other horizontal members to compensate but still not enough! Running on air even, I could see these frames that I could barely lift, flexing from side to side! I solved that by welding in more stretchers and all was well, until.... You see those big brackets under the middle of the tanks? They show very clearly in this builders photo at the Fowler Works (Credit: MERL collection) For a while I left the bolts out of these - they were a pain to put in from inside the tanks. Next time I had the engine apart - shown here having the steel boiler replaced with a new copper one - I noticed shiny metal and marks in the paint showing those brackets moving side to side by about a 1/16". I learned that day that those brackets were not to hold up a tank full water - the tanks were an integral part of the frame!
|
|
JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,902
|
Post by JonL on Sept 26, 2020 2:00:30 GMT
My goodness that Beyer Peacock is a beautful loco, which your engineering gives credit to.
|
|
|
Post by suctionhose on Sept 26, 2020 2:26:56 GMT
I agree. Beyer Peacock made some beautiful engines. Classic architecture of 1890. This is the original unsuperheated form which I so like the short smokebox and great deck out the front. The superheated ones had extended smokeboxes, lost that deck and gained ugly great turret tenders... Better engines for sure but lost the appeal for me!
|
|
oldnorton
Statesman
5" gauge LMS enthusiast
Posts: 688
|
Post by oldnorton on Sept 26, 2020 13:05:50 GMT
Good illustrations Ross of how extra plates and parts have stiffened up those models, and nice examples as well.
|
|