Strictly.... “ Hot Air “

[Alyn Foundry]

I've discovered that the " construction notes " for the half scale Robinson hot air engine have been misplaced.

There should have been construction notes     I didn't get any   

Jo

Yes Jo, three A4 sheets of them....

Hopefully someone might be able to find them?  A gentleman named Nigel McBurney ( hope I've spelled his surname correctly? )  bought several from me. I dropped out of the scene following my heart attacks, lost track of many friends and contacts.

Cheers Graham.

[Jasonb]

Managed to make my version without any notes, probably easier to direct any potential builders to threads on here that are likely to have a lot more info

[Twizseven]

Jo,

Graham has possibly just realised as I have just agreed to have a set of these castings off him

Construction notes would certainly be useful for idiot like me.

I have just printed out each of the views from the .pdf onto A3 sheets so I can try and read the dimensions

Colin

[Jo]

This thread is the construction notes  . My build started here: https://www.modelenginemaker.com/index.php/topic,7561.msg181544.html#msg181544

Jo

[Twizseven]

Jo,

Just finished reading all way through and making a few notes on the plans.

Yours looks very good and runs well on that candle.

Colin

[Twizseven]

Hope to start my Hot Air engine in the not too distant future.

Spent most of last few months finalising the sale of my Dad's house (plus sorting out Pension and Insurance claim stuff for him), am part way through having bathroom completely rebuilt (had to move wall and next week will have to fit new skirting and architraves to the doors, prior to plumber installing everything.), sorted out my machine tooling a little bit (into a Versatool cabinet), helping eldest daughter with her new house and garden, and have almost finished installing a crane to pick up the indexer and rotary tables for the Milling Machine.  At the moment the crane flexes the 48mm vertical steel tube it is mounted on and so needs a further support under the swinging arm.  Material is cut to length and ready for machining.

I have been though this thread again and adding to the notes I have made on the plans.

I notice everyone skips over anything concerning the brass/gunmetal parallel linkage.  Has everyone just spent a number of hours with small files and filed them flat and filed the bosses to a cleaner shape to remove as much of the casting marks as they wish.

Colin

[Jo]

I notice everyone skips over anything concerning the brass/gunmetal parallel linkage.  Has everyone just spent a number of hours with small files and filed them flat and filed the bosses to a cleaner shape to remove as much of the casting marks as they wish.

Yup that is about it. The actual lengths do not matter  other than the pair of links must be the same distance between the pivots.

Jo

[Jasonb]

Rather than hours with a file you could ream the holes and then mount them on the rotary table and give them a good clean up, not a lot of difference to how I cut mine from solid. A corner radius milling cutter would leave a small internal fillet around the bosses if you want to keep the cast look.

[Twizseven]

Jo, Jason,

Thank you both for quick responses.  I quite like the idea of the rotary table option but will find something to practice on first.

Colin

[ettingtonliam]

I cleaned them up with files and a Dremel, then superglued the link pairs back to back for drilling/reaming.  I've turned some buttons from silver steel to act a filing guides for the bosses.

The rotary table is overthinking the problem a bit IMHO. 

[Twizseven]

Finally started my Robinson Hot Air Engine.

Decided to start with the brass linkages.  Cleaned up with combination of files and the die filer.  Recommendations for the drop links to the regenerator and the con rods is to drill and ream them as pairs.  Cleaned the back faces of all of them with file and abranet on die filer table.  Miked up the bosses on the Regen links and it was touch and go as to whether I could get them to the requisite 0.2969.   I machined the boss faces on the small Cowells mill.  Basically nice and easy to see to work and in the warmth in my office.   The final dimensions were about 4 thou shy, but this will not cause a problem.

The con rods need to be .250  thick so clamped them flat on the table, used cigarette paper to align cutter with table top and dropped the knee 0.249 to give me the .250.  Repeated exercise for the second con rod.

Then came the fun bit.  Trying to superglue the pairs together.  The Regen pair took two attempts and the conrods three.  The first attempt on the conrod ended up in the gas hob to warm it up to separate the pair.  Eventually I was happy with them.

Back up to the Cowells Mill to clean up the sides of both pairs.

Tomorrow will hopefully drill and tap the holes for big end bolts and try and find a thin slitting saw blade to split the big ends.

Colin

[Twizseven]

Conrod was quite an awkward thing to mount because of the taper along its length.  After a bit of thought I remembered a Myford vice I have which has a swivelling section which can be used with the moving jaw moving jaw.  Was able to rest it on a paralllel and clamp up tight.  Then mounted the vice to angle plate on mill table.  I had made a couple of filing buttons and used one to locate the centre of the small end and put in a small dimple with a drill.  The Big end I had used calipers to find the center.  The only way I could think to get it vertical was to use the laser edge finder to pick up the line on the vertical face and the dimple in the big end. A sheet on white paper held at 90 degrees to the conrod enabled me with a magnifying glass to centre the laser The vice needed a few light taps to get this correct.  But eventually got there.

Centralised the X axis DRO on the glued split line, and the zeroed the Y axis on the center of the rod. Used a 1/4" endmill to create flat platforms on the what would become the big end cap.  Then swapped to 2.3mm drill to to drill two holes per cap ready to tap 2BA.  Went to depth of 8.5mm but this turned out not to be deep enough I found a bit later.  Tapped the holes to depth. Then drilled clearance hole to depth of big end cap.  Then hunted for thinnest slitting saw blade I had.  I had an arbor I had made for the Cowells mill and this just gave me enough depth to be able to line the blade up on the centre of the dimple in the small end.  Hand magnifier and bright light needed for this.  I had to remove the clamp I had in place whilst drilling to be able to use the slitting saw.  Lowered the knee 1.625inches and cut of the big end cap. This was when I found the drilled holes were not quite deep enough.  Was able to go round them all again with 2.3mm drill and then tap. All OK.  Cleaned edges of big end cap and refitted it temporarily with some long 2BA bolts with a nut and washer fitted to pull the cap down.

Next job drill and ream big and little end.

Anyone who has any better ideas as to how I could have mounted this up to machine it, please shout up.

[Alyn Foundry]

Progressing nicely Colin.

For the folk interested in the historical....

The first Robinson patent was issued in the late 1880's. I have attached some early written information. It would appear that the firms Norris and Henty and Potts and company were some of the first manufacturers.

The last picture is of 3 different sizes listed in the literature.

Cheers Graham.

[Twizseven]

Taken 3 days but finally got the brass linkages drill, tapped and reamed as necessary.

The superglue trick is all very well so long as it does not separate whilst drilling.  Which it did.  Carefully stepping up drill sizes and it suddenly snatched separated the glue but luckily the conrod in this case stayed with the drill.  My temporary big end bolts took a bit of a hammering.  Carefully reassembled back in vice and continued.  Unfortunately not too carefully.  What I had not notices was the lower conrod had tipped slightly.  Only spotted this after reaming the holes (0.250") and wondering why it appeared to be at an angle.  Bugger   Luckily was able to get the miniature boring head to bore the holes out from the required 0.250" up to just under 0.2812 (9/32") and then reamed 9/32".  Will now have heavy duty crankpin.

The two long straight links also separated the super glue and I ended up with a bent link.  Judicious use of arbor press restored it to straight.  I drilled/tapped and reamed these as individual links rather than as a pair.

Everything else went well.

One thing is certain it takes a damn sight longer to set these little things up to machine than the actual machining itself.

Now to make the pins.

Colin

[Alyn Foundry]

They look very nice Colin.

That's undoubtedly the most tedious of the engines construction out of the way, however I found the pin making equally so too.

The rest is fairly easy but don't forget to do all the facing operations on the cylinder before boring.   

Cheers Graham.