Stuart Twin Victoria (Princess Royal) Mill Engine

Don’t you turn the bore until it cleans up, measure it, and increment the tool outwards by half the difference to final diameter? I can see why a flat would make tool extension measurement more accurate, but not how turning cylindrical would help, unless it’s for absolute rather than relative measurement?

You can do it either way but having the section of bar true to the axis means it's there ready to make use of, also some of my bars are from quite rough hot rolled material so you would be measuring on an uneven surface which won't be very consistent.

As for overlength bar I sometimes drive with the chuck and just support the tailstock end with the ctr so you can put more of the bar into the chuck if it's too long but it does save having to keep making bars when the next longer job comes along.

Ok understood, thanks.

So this is the first attempt. I did shorten it a bit - I can't see doing anything longer than the P.R. cylinders, and wanted to maximise stiffness. I've still got a couple of inches each side of the cylinder to play with:



I didn't have a 6BA tap, so used 7BA for the adjusting screw instead. The locking grub screw is M5 - might need turning down a bit because I think it will touch the bore as it is. The tool hole is drilled at 6mm, and the spare stubs that Ramon sent me are a snug fit in it. The adjuster thread is 4mm long, the tool bore 14mm long. I did turn the middle true - it wasn't really out at all, and I'm not particularly proud of the finish I got, but I don't suppose it matters. Also milled the flat for measuring, and another for the carrier:







I also found a 3/4" carrier in a box of stuff I got with the lathe, which cleaned up nicely. If it doesn't work at least I've got a nice steam punk hammer:



Now to grind a few tool bits. I'm wondering if I should make a grinding holder for them out of perhaps square bar - I think holding by hand isn't really on, and grips might burr the surface such that it might not fit in its socket?

So I 3D printed a grinding jig, which I temporarily fitted in front of the bench grinder. I've graduated the angle markers at 10 degrees (they still need filling with white Milliput), and I'm hoping absolute accuracy isn't essential for this:



Is it acceptable to use the side of the wheel for grinding? If not, I think I need to make another recess in the table 90 degrees to the existing one.

Also made a holder for the 6mm diameter bits that Ramon sent me - my fingers were getting burned without it:



I have followed Jason's diagrams, but I'd like some comments on accuracy, surface finish, whether it needs a tip radius, whether it needs further finishing with the diamond files, or anything else that's relevant. I've never ground tools before, and don't want to ruin a casting through not grinding the them accurately enough. Here is where I am:

















Have I ground this in the right orientation? The intention was to set up as shown, and move the cylinder on the cross slide from left to right (chuck would be on the left of these images:





I'm not even sure how the tool should be orientated in the bar, and which surfaces are is doing the cutting! Does centre height setting apply to this method, if so, how to you adjust it? As I said, any and all advice gratefully received.

Thanks.

Edited By Dr_GMJN on 11/04/2021 13:10:51

Looks about right.

Just make sure that the bottom of the tool arrowed in blue does not rub against the edge of the hole

Its the arrowed edge that does the cutting and that's the one you could give a run to with a diamond slip

Best to avoid using teh side of teh wheel if you can

OK thanks Jason.

So I'll make a couple more for good luck, touch the edge up with the diamond file, and also grind them to the correct length.

On the last photo I posted, should the tool be rotated anti-clockwise slightly? I noticed the flat behind the cutting edge was angled down in the grinding drawing, but obviously you can orientate it how you want in the bar.

Just got to do some car work this week, then I can finally make a start on this one.

Yes you want the top face sloping down slightly from the cutting edge as shown in green but make sure the red clearance angle is not lost as you rotate it, you want both to be about 5degrees

OK.

when filing the edges, am I aiming for a sharp angle, with no edge or tip radius at all?

Also, how long will the bit stay sharp? Should I re-file it after every cut, or perhaps before the final couple of cuts?

Thanks.

I don't round mine.

Yes once you are close give it a lick with the diamond so it's good and sharp for the last couple of cuts.

Ok thanks.

Hi Doc , been out of it for a few days (plastic distraction) so only just caught up with your progress. Nice work on the boring bar and you initial tool grinding. You might find a holder made from round bar more beneficial in creating angles but those you've got so far look just fine. I would use the sharp tip as per the last image for getting under the skin but for a really good finish 'off the tool' on the last ten thou or so I'd grind (not file) a nice radius on that corner.

Keep the speed and feed well down for best results.

Looking good - go for it

Ramon

Thanks Ramon. I’ve taken a week off work for gardening and changing the rear brakes on the car. Unfortunately the easiest way to change inboard brake callipers is to remove the entire IRS. Got it removed today with the boy helping, next up is swapping the pots and re-fitting without getting squashed.

After that’s done, it’ll be full steam ahead on the P.R., although I’m still battling with an Airfix Swordfish. Shame they decided to put a massive pocket under the upper wing, that results in some subtle but very difficult to remove sink marks. It’s already been in caustic soda once...

Edited By Dr_GMJN on 12/04/2021 22:15:04

So it’s the one year anniversary of starting the 10V, so I made a start on this one. This time with some help from my son:



We got the castings and bed material out - shows how much work this is going to be:



After re-figuring out how all the 3D printed jigs were supposed to work, fist job was to trim the bed plate sides to length on the mill:



Small start, but it’s a start.



Next job is to co-ordinate drill the counterbored holes.

Good to see this one underway.

+1 : I've been looking forward to seeing this build

Thanks both.

Got the holes drilled and counterbored tonight; they all match - so far.







Very easy to get them mixed up, I’ll have to keep the markings clear to prevent a time consuming mistake.

Still have to drill sockets for the linkage bosses in the inner walls (B & C), then we will see if the 3D printed casting draft jigs work...

Decided to get on with the bed cross-pieces and ends. First job: saw 8x blocks a bit oversized, and de-burr:





Then machine to the right width with the shell mill. This wasn’t as easy as it seemed for some reason, and took several goes to get the corners 90 degrees according to the engineer’s square:



I’d machined an end stop for the vice during my dormant modelling phase, and this came in handy as a fixture for the 32 drilled and tapped holes:





Because of the way I’d designed the ends to allow for tapered outer faces, the holes aren’t on the central axis of the end pieces, they are offset inwards slightly. This tripped me up on the first piece, which gave a staggered end:



another lesson learned. I JB Welded some aluminium rod into the holes, faced off and re-drilled. It’s spot-on now.



Then the middle spacers were drilled and tapped, and reduced in height by 5.4mm:





Made another error by drilling the first hole M4 as per the ends, should be M3 to accommodate the taper. Silly error, especially when using my own design/drawings. Anyway, as with the ends, I realised after the first one, and that’ll be corrected by tomorrow. So here we are now:





Next job is to disassemble again, and drill a couple of blind holes in the inner sides for the bosses for the throttle bell cranks, then it’ll be machining the tapers on all the components.

So this evening’s job was machining the middle bed spacers to thickness:



Then machining on the simulated casting draw taper. This was a good opportunity for the boy to apply the trigonometry He’s only just done in maths at school. No problem at all - measured the hypotenuse:



And worked out the depth of spacer needed to tilt the vice at 1.5 degrees. Good example of using trig, good timing too.





So we found some scrap, raised the vice and cut the first sides:



Then came the confusion. My assumption was that to get a symmetrical 3 degree taper on the blocks, all we had to do was machine 1.5 degrees on one face, flip it in the vice and machine the other face. I’d assumed that the 1.5 degree face would add to the 1.5 degree vice tilt, giving an overall 3 degrees. When I told him to do this he was having none of it; said it would either give zero degrees, or an asymmetric taper, and that we needed a 3 degree tilt for the second cut. Somewhat taken aback, I decided to prove my point with 2D CAD. Turns out he was right I think.

So we put one of the 3D printed 3 degree wedges I’d made for the long sides under the vice:



And cut the faces:



And they turned out spot-on:



They just need rounds filing on the top edges.

So I suppose the moral is, don’t assume your student necessarily knows less than you.

You are both making good progress, just watch those hoodie strings around machines.

Thanks Jason - very good point about the strings. I should have noticed that before now.