My James Coombes

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My James Coombes

This topic has 12 replies, 4 voices, and was last updated 15 June 2015 at 11:03 by lancelot.

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19 July 2014 at 21:35 #158264
lancelot
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@lancelot
This is what I am building at present…thanks guys for the info on the chuck I will have to stick a notice on the wall beside the lathe

Cheers,

John.
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19 July 2014 at 21:35 #31058
lancelot
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@lancelot
20 July 2014 at 10:09 #158290
lancelot
Participant
@lancelot
Got the drawing for the Coombes on Saturday a/m…spent some time checking all the bits and pieces that I have made to the drawing (new) [which now takes precedence over all earlier drawings…including those in the book.]Also bearing in mind what Peter Southworth the Corliss Guru who knew a lot about those engines…when I asked him once about a possible problem with a casting set up…his answer was ''the drawings are only a Guide, Make the parts Fit'' an interesting if not unique reply.As you may have surmised from this there is a slight difference of opinion in a measurement but some careful forward planning should sort any potential probs… all the best for now

John.
23 July 2014 at 15:38 #158568
lancelot
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@lancelot
Having a bit of trouble with the Cross head frame slot …found it to be well chilled,milling cutters ,no way…So I set up a Diamond router (for C/F use)..Clocked in each end of slide and let rip with the cutter very S L O W but a great job on the first slide frame There was a little warming up of the mill head bearing so closed down for a while…back later.

John
23 July 2014 at 19:55 #158581
Steve Withnell
Participant
@stevewithnell34426
Hi John,

I was planning to clamp the frames together and mill both slots at one setting. The outer edges were very easy with a file not hard at all. The overall finish of the raw castings was about as smooth as a bear's bum.

When did Stuarts ship your castings?

In any event they should replace them if they will not machine nicely, they have always had a good rep for replacing any dodgy castings. I was going to send mine back, but given they seem easy to work, it's simpler to put a but of extra effort in to cleaning them up.

Steve
23 July 2014 at 20:31 #158583
lancelot
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@lancelot
Hi Steve, I swapped them on ebay …I got a set of Coombes castings and other bits and bobs …He got a Tich loco at about 50% build stage (still have the Kennions Large 3 1/2 '' copper boiler)… I found no problems with the castings …the valve chest and cylinder boring quite straight forwards cutting the slot with the Diamond tooling leaves a great finish ,but it is very slow and I do not want to strain the wee cowells overly much.

I intend to leave the castings in the sandpaper finish they are in, when sprayed with etching primer the finish looks really good..

All the best for now,

John.
25 July 2014 at 20:24 #158733
lancelot
Participant
@lancelot
Finished grinding the slots now working on the sliding bearings that fit them…noticed a bit of heating up in the machine spindle bearing area also in the motor …had a talk with Colin Childs describing the areas and heat intensity…No need to worry,the wee machine performed brilliantly…Job Done.

John.
14 June 2015 at 17:32 #193423
lancelot
Participant
@lancelot
Hi folks… back again to say the Coombes is completed……..But….It will not start….She tries with approx. 50 lbs pressure kicking over almost 70% of a rev…with speed and power I have checked all linkages for looseness the timing has been reset umpteen times ……no joy….I started this build way back ,with a 2 year break then had to obtain new drawings issued 1993…which show the offset for the occilator sheave as 9/64'' this drawing supercedes all the others and the book which shows it as 11/64'' …I have made mine at 9/64''………I have found that this does not allow for the inlet valves to open to their full capacity and are only opening part way top and bottom this makes trying to set the timing very difficult…

Would certainly appreciate your comments and ideas on this on…

All the best for now …

John lancelot
14 June 2015 at 19:01 #193433
JasonB
Moderator
@jasonb
What spacings have you used for the valve ports?
14 June 2015 at 20:15 #193441
lancelot
Participant
@lancelot
Hi Jason…if I am reading your question correctly drawing 1993 issue shows dimens ..(.on my cylinder holes for ports were already in p;ace ) inlet ports 3/32'' top and bottom exhaust port 3/16'' the exhaust port just happens to be exactly in line with the outlet on the side of the cylinder which gives a chance of running into on of the 7 ba stud holes …I user a DENTAL drill point to drill a sort of curved connecting hole and still managed to just touch on the stud hole…..

the distance between the top and bottom inlet ports is 3/8''the centre line of the exhaust port lies on two middle valve chest stud holes

cheers John……lancelot.
14 June 2015 at 20:48 #193442
JasonB
Moderator
@jasonb
Should work OK with thoise spacings and the 9/32" throw, thats what I used on my beam engine which has a lot of similar parts.

J
14 June 2015 at 21:41 #193445
Nick_G
Participant
@nick_g
.

Is the slide valve 'free floating' so that it mates with the inlets on the cylinder when pressure is introduced into the valve chest.?

And have you got the slide valve in the correct orientation.? – There are 2 possibilities for this 1 right and 1 wrong and could cause problems with setting up the timings.

I asked the same question here :- **LINK**

Nick
15 June 2015 at 11:03 #193490
lancelot
Participant
@lancelot
Hi folks…just off phone with Stuarts their guy said allseems right in my build 9/64'' should let it run but same as you Nick check inlet ports for sand blockage which would give it that back pressure ''thump''

back soon…

John.
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