rocking grates

[peterdanastas]

Hello All, I am building a 5"Britannia to Doug Hewsen design and it shows a rocking grate. As I have no experence with rocking grates in minuture scale only full size rocking grates. I am wondering if they are troublesome in jamming up when trying to open and shut. Any thoughts or suggestions please before I proceed in building a rocking grate . Also on the Britannia you cannot remove the ashpan and if you build bar grates you have to make in sections as to remove from firehole door.

[oldnorton]

I wish you every success with this build, it is the ultimate 5" Britannia. I used Doug's excellent drawing set to fully 'Hewsonize' my Modelworks engine a few years ago. I wonder if you and I discussed this grate question a while back at Cinderbarrow?

You will know the Britannia grate issues so I will only repeat these to help other readers not familiar with the design. To drop the grate out through the bottom (or even pieces of grate) is almost impossible on the 5" Britannia because of the two frame sections that run back through the ashpan. For this reason some have tried a grate that slides out from the side.

A sectioned grate only works if the longitudinal sections fit through the firehole, and different boiler designs have different sized fireholes. The later Modelworks boilers have the largest firehole and my Britannia grate is in three longitudinal sections. Normally, I shovel the hot fire out at the end of a run, then when cold I will use a vacuum cleaner to remove everything left behind. After a few runs I will take out the grate sections, through the fire door, and do a further clean. Taking out and replacing can be a one hour job and not something you want to do if it is all hot.

Of interest, I did make a drop door in the centre grate section so that I could push the fire out through the centre ashpan door. This worked well from new about four or five times, then it all jammed up!

A Perrier firedoor size needs four grate sections. If this was something you wanted you need to check on Doug's size of firedoor and whether four sections will still fit through.

I have not spoken to anyone who has made the Britannia rocking grate and tried it, but Doug did design a rocking grate for his Standard 4. The problem is that all the mechanism is so prototypical that it is not strong enough. I know of a Hewson Standard 4 grate that jammed up on its very first steaming and the boiler had to come off. I will not say whose engine it was. You can be almost certain that a rocking grate will give problems at some point. Then, the only repair is to lift the boiler and remove the ashpan - doable but a two or three-day job.

If it was me I would persist with the rocking grate, but make all the action and levers as tough as possible so that enough leverage can be exerted to crush any jammed ash lumps. In conjunction with a vacuum tube through the firedoor any problems could be worked free. Also, make any rotating shafts in bearings as slack as possible (0.020" or more free play) so that ash can be shaken or blown out. When the inevitable happens, and hopefully it jams in the closed position, just vacuum the firebox clean after a run until the season end when the boiler lift has to happen.

Norm

[Jim]

I solved the problem by making a slide in slide out grate for my Britannia and it works well.

Jim

[chris vine]

On my B1 I made a dropping grate but much tougher than scale. A compromise between scale and robustness for running.
However I just vacuum out the old fire when it’s cold so have never used the dropping action once.
As long as what you make is robust and you can slide it out in some manner to replace bits if they burn, then I would go with that. You could even add some blobs and gadgets to look the part…
Chris

[peterdanastas]

How does the rosebud grate perform jim

[Jim]

I'm happy with it Peter.

You can get the technical details by Googling Rosebud Grates and it's dead easy to remove while dropping the fire/ash at the same time.

This is one of the sites that comes up:

altrish.co.uk/2018/07/26/calculator-for-rosebud-grates-for-live-steam-locomotives/

Jim.

[johan]

Nov 9, 2024 21:15:03 GMT Jim said:

I solved the problem by making a slide in slide out grate for my Britannia and it works well.

I read the link in the last post and I'm wondering about the 15% air openings. That seems low to me compared to all other grates.

[peterdanastas]

Hello Jim it is a long time i spoke to you . I have studied your idea and it is good but I have injector valves and injectors in the road . When the boiler was built I have got a larger fire hole in it and I am going to go with 3 bar grates as the hole is slightly over2 inches and I will stay with the 2 fixed sections of grate on the outside and 3 removable grates on the inside.I know I will have to put the dampers in the ash pan as I may have too much draft going threw. I have a King loco and it has a long narrow fire box and you have to fire often with little coal. The draft on it could be slightly better as you got to be ready to regulate the blower.You have to fire it like you hate it and I hope the Britannia will be a lot friendlier to fire. I know bar grates are old school and a pain to remove after the run day to clean but like some one said shovel ouy most of coal and hold your tongue when removing

[simon6200]

In practice 15% air works well. Easy to test: just drill a piece of 10 mm steel and give it a try. I make them a close fit in the firebox. For me it is essential to be able to pull a pin and have the grate and ashpan drop out. I rearranged the brake gear on my Springbok to leave the area clear and omitted the steam cylinder in favour of a 3 kg block of lead. Not so easy with a trailing truck of course but Jim’s slide out grate looks good.