Post by baggo on Sept 13, 2010 10:07:11 GMT
One of the 'projects' I'm working on at the moment is the cylinder assembly for an Allchin TE. I was approached by some one who had bought a part built Allchin from Ebay but did not have the facilities to complete some of the work required.
It's one of those projects that has been through at least 2 sets of hands as a lot of the work is to a good standard but the later work is pretty poor. The cylinder required major repairs and remachining, but that's another story!
Part of the job was to finish off the trunk guide. This had originally been machined very well but then some one had fitted the motion bracket to the wrong side! The new owner had managed to get the trunk guide 'repaired' by welding over the steps already machined for the motion bracket. The welder had made a very good job but unfortunately, the casting had gone banana shaped and I wasn't sure if it could be salvaged.
The new owner was happy to supply a new casting but I decided to have a go at fabricating one from scratch using mild steel. It would be an interesting project and would save the owner some money!
The main body of the guide was machined from 1.25" steel bar and rough bored before parting off to length.
The bolting flange was machined from 3/16" plate to allow for finishing to size and then silver soldered to the body.
A quick clean up of the joint
The sides were then milled away. The easiest way to hold the 'casting' was to clamp it between two angle plates using a long bolt.
The oil pot and bottom bracket added
The inside of the slots now needed machining. My copy of the book for the Allchin is missing an illustration that shows how this is done and the description is a bit confusing without it!
Firstly, the edges of the slot are machined vertically with a 3/4" endmill to leave the bearing surface for the crosshead at 9/16" wide. The book says use a 1/4" endmill which is wrong! The original ME articles do contain the illustration and the endmill size is correctly given.
The outside corners are then angled off with a small, say 1/4", endmill. The guide is rotated at 50 degrees for this. I used a cardboard template to set the guide to this angle.
The inside of the guide was then finished bored to size. I left this operation till last as I thought the body may possibly distort during the silver soldering and the machining of the slots.
The bearing surface was bored with the guide set up to run truly in the 4 jaw and with the outer end supported in the fixed steady.
The cylinder end was bored by mounting the guide on a mandrel machined in situ to a very good fit in the already bored section. To prevent the guide slipping, I lightly clamped it to the mandrel with a Jubilee clip! The bolting flange was also faced off to thickness and the outside diameter finished.
It's essential that the bore of the guide is perfectly square and concentric to the bolting flange if the crosshead is to run freely.
Nearly finished! Just needs the edges of the slots rounding off with a file
Next job is to fit the motion bracket (on the right side this time or should it be the left!)
John
It's one of those projects that has been through at least 2 sets of hands as a lot of the work is to a good standard but the later work is pretty poor. The cylinder required major repairs and remachining, but that's another story!
Part of the job was to finish off the trunk guide. This had originally been machined very well but then some one had fitted the motion bracket to the wrong side! The new owner had managed to get the trunk guide 'repaired' by welding over the steps already machined for the motion bracket. The welder had made a very good job but unfortunately, the casting had gone banana shaped and I wasn't sure if it could be salvaged.
The new owner was happy to supply a new casting but I decided to have a go at fabricating one from scratch using mild steel. It would be an interesting project and would save the owner some money!
The main body of the guide was machined from 1.25" steel bar and rough bored before parting off to length.
The bolting flange was machined from 3/16" plate to allow for finishing to size and then silver soldered to the body.
A quick clean up of the joint
The sides were then milled away. The easiest way to hold the 'casting' was to clamp it between two angle plates using a long bolt.
The oil pot and bottom bracket added
The inside of the slots now needed machining. My copy of the book for the Allchin is missing an illustration that shows how this is done and the description is a bit confusing without it!
Firstly, the edges of the slot are machined vertically with a 3/4" endmill to leave the bearing surface for the crosshead at 9/16" wide. The book says use a 1/4" endmill which is wrong! The original ME articles do contain the illustration and the endmill size is correctly given.
The outside corners are then angled off with a small, say 1/4", endmill. The guide is rotated at 50 degrees for this. I used a cardboard template to set the guide to this angle.
The inside of the guide was then finished bored to size. I left this operation till last as I thought the body may possibly distort during the silver soldering and the machining of the slots.
The bearing surface was bored with the guide set up to run truly in the 4 jaw and with the outer end supported in the fixed steady.
The cylinder end was bored by mounting the guide on a mandrel machined in situ to a very good fit in the already bored section. To prevent the guide slipping, I lightly clamped it to the mandrel with a Jubilee clip! The bolting flange was also faced off to thickness and the outside diameter finished.
It's essential that the bore of the guide is perfectly square and concentric to the bolting flange if the crosshead is to run freely.
Nearly finished! Just needs the edges of the slots rounding off with a file
Next job is to fit the motion bracket (on the right side this time or should it be the left!)
John
That was soon put right though by drilling and reaming the bore oversize to realign it and then fitting a bush to bring it back to size.
