Correcting an off bored cylinder

Hi All,

I have a Stuart Victoria cylinder that i bored off center and the end flanges are faced to match....i want to correct it and i think there just about enough meat to bore out bigger and increase the piston size.

Question is - how best to set it up in the 4-jaw squarely in order to make the correction....i effectively have no reference face.

Thanks

Matt

Here are a few photos....

I would now get a flat surface on the valve side so its square to the two ends. I would then mount it on the cross slide, pack and clock the existing hole for parallel and mount a adjustable boring tool in the chuck. But thats my opinion I will be interested how others would do this.

Edited By BOB BLACKSHAW on 23/03/2018 01:36:50

A better way would be to mount the cylinder on a angle plate, then a boring bar between two centers using a lathe dog would be more accurate.

Is the hole in your chuck bigger than the cylinder hole? If so, turn and bore a piece of round or flat stock that plugs into the centre register of the chuck and superglue in in place on the flat end of the cylinder. Now use that plate to locate the cylinder centrally on the chuck, hold it tight against the chuck face using the tailstock ram and and snug up the four jaws with the soft packing until you have it held for boring.

In that situation without access to a mill I might be inclined to mount a boring head in the headstock and mount the casting on the cross slide in the fashion of the Old School Myford users

Either way you need to make small (eg Al) plugs fro each end that you can mark the new required centre in for setting up. When starting to bore the new hole ensure you are using a tool that cuts on the end, that is not a V or angled end. You need the forces to be entirely in the direction of the hole otherwise as it cuts in the existing hole the depth of cut will vary and the sideways force will vary bending the tool away from the cut and resulting in an oval hole.

Turn a disc of metal, it matters not a jot what it is to a dia slightly smaller than the end flange of the cylinder. Drill a hole in the centre of about 7mm, the disc should be about 6mm thick. Now place the disc on the end of the cylinder with a length of 6mm studding passing through the bore. A strip of steel or whatever with a tapped hole in should act as a nut on the other end, this strip should as you no doubt realise bridge the bore, a nut on the outer end secures the whole lot in position. Set up in the lathe as before and clock the disc to run true. Undo the nut, using the biggest boring bar you can pass through the bore, bore to size. Job done, don't forget to just skim the face to ensure it is square to the bore.

Edited By Dusty on 23/03/2018 10:15:23

The suggestions so far seem to overcomplicate the issue, There was nothing wrong with the original boring technique other than the hole was in the wrong place. As I understand it Matt wants to redo the bore as near as he can to the correct place.

The correct position is presumably concentric to the OD of the casting end flanges. The only thing that confuses me is why he mentions that he has no reference face?

Since we can see at least one end of the casting has been machined normal to the axis, then that face could be placed flat against the faceplate (preferably on a large 'washer' and fixed in position with three clamping plates bearing on the cylinder casting flange. The large washer would have a clearance hole so that the tip of the boring bar can pass completely through.

Ian P

Traditional way is to fit a wooden plug in the bore and face it smooth, then find the centre and mark it, use this as a reference point to set up in 4-jaw, remove plug and away you go.

Lazy man's way (mine) is to align the job so the tip of a tool lines up with the outside of the flange while the job is rotated by hand. If it looks near enough, the bore will be placed accurately enough.

If the end face was machined at the same setting as the bore which the OP suggests it was then I would not want to be using that to reset the work, the bore looks to run at an angle to the port face of the casting so that face will also be at an angle..

I would get the port face machined first and use that as the ref face. This can easily be done in the 4-jaw as two opposite jaw slots act like a Vee block for the flanges to sit in and a rule can be placed across the port face to get it at right angles to the lathes axis in the other direction. Now face the surface flat.

Ideally this flat face can then be held against an angle plate fixed to the faceplate to set the part square in one axis and a square used against the two flanges to set it true in the other axis before it is clamped tightly to the angle plate. You can now tap the lightly bolted angle plate about until the outside of the flange runs concentric and when it does tighten the angle plate to the faceplate and you are ready to bore and face. If you don't have an angle plate then the 4-jaw can be used with a square to ensure the port face is at right angles to the chuck face and also against the two flanges to make sure it is not twisted.

Plugging or clocking the flange is OK but you can't clock the other end true so end up with exactly what the OP has  - hole central to one flange and well off by the time it exits the other end.

J

PS this also happens to be the way all the Stuart booklets tell you how to machine a cylinder casting.

Edited By JasonB on 23/03/2018 12:28:26

Matt, assuming that the end faces are square to the slide face - then I'd super-glue a piece of brass to one end of the cylinder and then find the cylinder centre from the external edge. This can be done on a surface plate using a height gauge (or even a simple scriber). 'Pop' it gently and then centre the casting in the 4-jaw as before (using two lathe centres - I'll post a photo of a similar set-up). Then gently knock the brass off sideways without disturbing the setting.

As IanP says - you can simply then just re-bore it, using a washer or some such to allow end clearance for the boring bit. If your current eccentric hole isn't 'true' (e.g. runs at a slight angle) you may find the new hole may need to be larger than you think - worth checking carefully before you start.

Regards,

IanT

Is the bore just too far away from the port face, but otherwise okay?

If so then I'd mill the port face to get it flat, then set up in the 4 jaw as you have and do as Neil says - use the outside of the cylinder flange as your "reference" checking it is running as true as you're happy to get it and rebore just enough so you stop when the tool just cuts the old bore furthest away from the port face. That way you'll bring the bore closer to the port face but not any closer to the opposite side of the casting.

OK, so its off centre. You don't say by how much. Could you adjust the frames/ structure to accommodate. Ie, skim a little off the frames where the cylinder bolts onto it, or adjust the mounting holes etc ?
BobH

I can see there is not machined valve side.. common new beginner fault..

1. Valve side machined to flat surface who are in same height as in center of bore in both sides of cylinder.

2. Set up on angle plate who are mounted on lathe and adjust center of bore and cylinder in parallel with lathe.

3. Turn flat on the cylinder side who are bottom side of cylinder then bore the cylinder to right size. Mark up this with tiny punch dot at a place where the bottom side will be (This is correct in angle between cylinder /side of cylinder to preventing galling between piston/cylinder).

4. Turn the cylinder to other side and set the parallel tool to set bottom side of cylinder is in parallel with disc on lathe then turn the side of cylinder flat who are cylinder head side.

Edited By Jens Eirik Skogstad on 24/03/2018 07:28:37

David and Speedy, look at the photos and you will see that the bole is concentric to one flange which was no doubt the end facing out and was clocked true but the other end of the cylinder the hole is eccentric due to the part not being lined up along the lathe axis when bored.

So you can't adjust the structure unless you want a sloping rather than horizontal engine and if not set up correctly the second time with a flat port face you will still get an out of line bore

I think a replacement cylinder casting for the Stuart Victoria is about £20 plus VAT.

It might be worth considering starting from scratch if they are in stock.

Thankyou everyone for your comments.

Buying a new casting is an option, but i am in Canada and by the time i have paid for the part/shipment/broker fees/tax etc it will be equivalent to 50 quid. And, i have nothing to loose by trying to correct it....if i mess it up further, there is nothing lost

I see there are a number of ways to do this and correct the problem.....actually part of my problem is equipment i have available. For example - i do not have a faceplate nor true 90 degree angle bracket....perhaps i should invest!

One approach i have read and like the idea of is using a faceplate and a Keats angle plate. This looks a very easy way to correct the problem with easy adjustability whilst ensuring a true parallel setup......the other approach i thought of was to use a tube drilled and tapped with 3 screws at each end. The part could than be clamped and adjusted in the tube. The tube can then be fitted into the chuck and easily checked with a DTI.

Anyway - thanks for all the ideas, i will let you know how i get on!

Matt

Matt,

You can make a faceplate - if you want. All you need is a circular slice of metal that you can bolt to a lathe back-plate. It can be a piece of scrap plate that initially you cut to rough size and then turn down and face flat in the lathe if you cannot or don't want to purchase/find/source suitable diameter steel/cast-iron/wot-evah as the basis of your faceplate.

Similarly, using the lathe as a mill you can true-up your out-of-true angle bracket or make one yourself from a suitable piece of steel, (girder, bracket, welded pieces, etc.). If making it yourself don't forget that, at a push, you only need to true the area to which the cylinder will actually be bolted/attached - & thus may save lots of tedious milling!!

Hopefully not suggesting solutions that = 'teaching grandma.. etc.,' Apologies if so.

Regards,

Phil

I think many of the suggestions are over complicated, just set it up in the 4 jaw with the outsides of both flanges running something like, then bore it out until it cleans up and face off the end which is accessible. The other end can be done on a manderl, but as long as it is the end away from the crankshaft squareness doesn't realy matter. Before starting you need to check there will be enough metal left on the end flange, as the bore will be oversize. Once you've achieved this put a bolt through the bore to hold the casting face down on your topslide and flycut the valve face, provided the face of the topslide is true it can't be wrong.

In your original photo ~4 you have hold of far too much in the chuck. You need to be able to set up both ends true, only grip about 5mm max, and dump the packing. Unless you are very patient it will keep falling out as you adjust the jaws. Use the biggest boring bar you can find to avoid it springing with the interrupted cut.