Stuart 10V Build Log - Complete Beginner...

No - But I like it.

Cheers!

I usually do the same as you did and slip a couple of parallels between chuck face and back of work

And remove them before machining, rather than securing them somehow?

Thanks.

Yes, 99% of the time I would remove them, on the odd occasion where there may not be much metal to grip and therefore a risk of the cut pushing the work back I will either wire or zip tie them in place

Edited By JasonB on 28/05/2020 17:36:43

OK great, so I used the same method as that tonight for the other handwheel block.

One change I made was to turn a brass spigot to knock into the existing bush in the block. The spigot had no measurable runout. I was able to easily center the block in the 4 jaw chuck using a DTI on the spigot so there was no measurable runout.

I'd centre drilled the spigot, so as an experiment, I used my centering rod again:



Again, just under 0.002" runout. No way I can get better than that. Even though I'm holding the rod to prevent it turning (if I let it turn it's worse - but no real surprise there), no matter what I do to the chuck, I always get that error; I got the same residual error when I put the point directly into the bush in the block yesterday. It can't be centering technique with the chuck, becasue I can easily zero it using a DTI on a known true cylinder.

Any thoughts on what I'm doing wrong here?

Anyhow, the block got machined - I calibrated the depth stop as suggested (but used calipers rather than slip gauges) - and the bearings were fitted. Both X & Y axes on the mill are now really smooth with minimal backlash.

Thanks!

If the spigot has zero runout then I would suspect the centering bar and where you are measuring on the bar, have you tried measuring  close up against the spigot?

I measure close up against where the bar contacts the part. 

Edited By Ron Laden on 29/05/2020 04:43:18

Ron - I’m measuring about 1” back along the bar from the part. Since I’m measuring wobble rather that runout of the bar itself (assuming I stop it rotating) I don’t get why I can’t zero it - presumably in theory it doesn’t matter where along the bar I measure, but the biggest reading will be nearest the workpiece?

I think your angle on the end of the rod may be the problem. A ctr drilled and even a spot drilled hole will have a very slight flat on the bottom, your ctr punch mark from the other day will leave a wide 90deg cone and again may not have a perfectly flat bottom.

Now your very sharp pointed low angled indicator rod will touch the bottom of your mark not and not sit taper to taper.

So I would suggest you recut the end taper to 60deg inclusive angle, use a dot (prick) punch which are also ground to 60deg and if drilling to mark the position then use a small BS0 ctr drill and go in all the way with the pilot plus a small amount of the part that cuts the 60deg seat.

One other thing to bear in mind when making something like that plug, if your 3 jaw is a bit out it is unlikely the hole is concentric to the OD of the plug. For a job like this where there is an existing hole you would be better off just setting the lever of the dti to run against the inside of the hole, save the rod for when there is no suitable hole.

Thanks Jason, OK I'll re-cut the point again to 60 degrees inclusive. And I'll re-turn a portion of the adjacent shaft too.

Is there a good way of re-profiling one of my centre punches to 60 degrees too?

BTW the punch holes so far are only in the bras bearings - for the spigot yesterday I did centre drill it to make sure the point didn't bottom out. The spigot was turned in a collet, but of course if the center drill wandered it wouldn't be central.

Also, I tried the bar in the existing through hole in the handwheel block, so it was in there to about half the taper depth (and obviously there was no bottom to it). Same story with runout.

Anyway, I'll re-cut it and try again.

I sacrificed a day on the 10V to make a tool board/shelf for the lathe and milling machines. I was wasting loads of time looking in my tool chest drawers for things. I’ve made it all slot together so I can quickly separate the two benches if I need to move them. Common tools like the collets and soft hammer are in the middle. I cut some aluminium angle up to put the lathe tool holders on.











[url|https://thumbsnap.com/oNw6VGNc[/url]



Quite pleased with that, especially since it was made out of scrap MDF so didn't cost anything.

I've sidetracked this thread a bit, but now back to the 10V - the main bearings.

I opted to go a bit off-piste, ignore the plan dimensions and mark the center of the cast semi-circle. My reasoning being that at the end of the day, if the turned bosses are not concentric with it, it’ll look wrong, and the specified dimensions are so close anyway, it won’t make any difference to the function of the engine.

My edge finder is 6mm diameter, so a fraction too large to take a direct measurement from the straight sides of the bosses. I decided to clamp both castings as shown, and calculate the centreline from the inside of the vice faces. Once locked in “y”, It was a simple task to offset from the exposed curved surfaces, and center drill them:







No idea if that’s a good way of doing it, but it made sense to me and it seemed to work.

Then onto the lathe to drill the crankshaft holes. I spent a good 45 minutes faffing about with shims in the 3 jaw chuck, and getting nowhere near true. In the end I cut some square spacers and used the 4 jaw chuck, and it was centred to less than 0.001” within a couple of minutes. I locally re-profiled my centering bar tip to 60 degrees included, and it seems OK now (thanks for the suggestion Jason!). Still needs holding to prevent rotation though:





I drilled them progressively up to 6.8mm. My plan is to line drill both bearings in-situ to 6.9mm, then ream in the same setup.

Wall thickness around the curved area is within about 0.004”. I doubt I could currently get any better, so that’s that.

Next up: make a mandrel and cut the bosses on the lathe.

I would not get in the habit of holding two parts at once in the vice like that. There is always the chance that one is not held as tightly as you think and will come loose when it is being machined. It is relying on the two parts being nearly/exactly the same width where they are gripped and the vice being sloppy enough to twist the moving jaw to even out the grip on the two parts. Copper and its alloys are grabby, the bearings could easily have been twisted out of the ends of the vice if a drill had been grabbed by the alloy. One at a time in the centre of the vice may seem a bit slower but it is going to give a better grip and twisting of the workpiece would be next to impossible. I would suggest a vice stop and parallels would help when you have more than one item to machine the same way. Parallels support the part solidly. Your method of holding them could cause them to be pushed downwards. If you had asked if it was a good setup to drill them I would have emphatically said no. Just for marking out is not a problem but it is something to think about for the future.

Martin C

Edited By Martin Connelly on 02/06/2020 09:30:10

Thanks Martin - understood; I wouldn't consider any significant machining operation while holding parts like that. My thoughts were:

1) The casting has been cut in half, and so the width is essentially the same for both parts - they measured exactly the same with my calipers. If they'd have measured differently I wouldn't have tried it, not least becasue as you say the jaws wouldn't have been parallel, which would have affected the reading, and not done the vice any good.

2) I was only centre drilling to a couple of mm, so very low forces involved.

On the face of it, it seemed like a good way of getting around the issue of not having enough room to find an edge.

Turned a bearing mandrel from some scrap brass rod, and threaded the end M5:



I made a spacer for the end, to the correct boss diameter, so I could easily see when I was nearly at the right size:



Marked up and cut:



I’ve never tried intermittent cuts on the lathe before, but it was fine.



I’ve polished to top surfaces with wet and dry on the surface plate, ready for drilling. Shame there are some surface flaws I can’t get rid of.



I left all the bosses long, so I could size them precisely to the crank webs and eccentric. Not sure how I’ll hold them for that - perhaps in the collet chuck, or modify my mandrel somehow.

All,

I'd like to put a very small chamfer around the top edge of the rectangular bearing plates. It looks like I've got about 1mm clearance between the top of the boss and the top surface, so a 0.5mm x 45 degree chamfer all around should be OK. I have a 45 degree chamfering tool.

I tried chamfering around my travel stop and it worked OK for what it was, but for this, I need to be very precise.

What I found with aluminium was it was difficult to determine when the tool had touched the edge of the work, becasue it was soft. I think it'll be similar with brass. If the chamfer is only 0.5mm, then any excess cut depth would give an inconsistent chamfer width.

Any tips for setting up this job for chamfering? I suppose everything has to be absolutely square and level before cutting, but these parts are quite small.

Thanks!

Probably quicker to file than set up and mill.

If you really want to machine it then a but of simple maths once you have located the edge, and end of tool should get a consistent result

Thanks Jason, so if machining, you'd calculate the offset to put into the machine, or would you mark out and cut up to the line? I was thinking that cutting to a line once the tool depth is set to give a small excess, it would eliminate any errors in initial setting when using the DROs.

I was going to mark out and file (might still do that), but the area around the top of the boss is difficult to access.

I would not mark it out. Though you could blue the whole thing to make it easier to see what you have cut as a double check.

OK, I'll ponder the chamfers a bit more while I get the holes drilled and the the bores reamed.

Jumping ahead a bit: the standard.

I've seen a couple of builds use a bolt to get a best-fit through the cast central hole, which makes sense to me becaue you use that setup to machine the feet flat:



I will probably cross-drill the bolt in the region of the oval cut-out, and knock a pin through to stop it rotating on the shank.

But then I want to turn the piece around and turn the bore, the cylinder face and the rim. The logical way seems to use a faceplate, I could even modify my existing vice clamps to secure it:



Question is, how do I center it accurately?

I thought about mounting it to a rectangular plate and mounting in a 4-jaw chuck, and centering it using the DTI on the protruding bolt shank, used as a temporary mandrel. I've seen online where the standard bore was machined offset from the casting axis , and even though in practical terms it might be OK, I really want to avoid that.

Any suggestions welcome!