Member postings for Andrew Johnston

Not really, although slightly less bending of the cable if it moves.

Andrew

I've got a 2-axis DRO on my Bridgeport, but nothing on the knee or quill. I find 2-axis fine; I've never missed a 3rd DRO axis.

Andrew

Not identical, but it is M12:

Cable Gland

Plenty of others on Farnell and I expect RS will be similar.

Andrew

One, calculate each point from basics, rather than incrementing a small, approximate, value. Two, chose a calculation/rounding method that gives a uniform spread of errors around the exact value. That way the accumulated error grows much more slowly than the accumulated value, assuming of course that the errors uncorrelated.

Andrew

Not so. The first 4 indicates protection against anything larger than 1mm. That's a pretty small finger. The second 4 is protection against splashing water from any direction. A quick look at the manual for the VFD I bought for my Pultra gives an IP rating of 20, which is common for items considered to be components that will be incorporated into a larger unit.

Andrew

I spotdrilled and then used a ballnose slotdrill in the lathe. With a range of metric and imperial slotdrills one can get pretty close to the actual size. Odd sizes, particularly 32nds or even 64ths, are often on Ebay at minimal cost.

I CNC milled and drilled my own spokes. The rivet patterns are copied from full size rather than the drawings. For the front wheels the 3 holes are on an arc, not a straight line. On the rear wheels the 4 rivets are zig-zag, not in a line. The rivets are 3/16" which is conveniently close to 2BA. The holes in the T-rings were marked out by hand. I scribed a circumference around the T-ring with oddleg calipers at the distance in determined by my 3D CAD model. I also knew the theoretical distance from spoke to spoke from the CAD model. I set that distance on dividers and stepped round the previously scribed line until I go back to the start. If everything didn't quite line up I adjusted the dividers and had another go. Once marked out I spot punched and drilled free hand using the vertical mill. I used a fixture to fit the spokes on each side in turn:

The hub is sitting on a spigot screwed to the plate. The rim is centred on the hub as best as possible with a rule. Note the 2BA screws. Once a set of spokes are fitted it is simple to drill through the other holes on the spokes. I drilled the spokes and T-rings 4.7mm, ie, a tad undersize. When riveting was underway I ran a 3/16" drill through each hole in the spoke/rim before fitting each rivet. Generally after drilling the rivets needed a slight tap with a brass rod to get them inserted.

Fitting the spokes on the rear wheels was similar except that the rims needed blocking up different amounts on each side, and on each wheel. Since the rear spokes are on the inside of the T-rings one can't spot through for the additional holes. I used a fixture based on a spare spoke and a block that straddled the fitted spoke. A 2BA bolt held everything together for drilling each spoke:

Generally the wheels won't fit on my 12" rotary table, but I did fudge it to drill one row of holes in the rim as a starter for the rear wheel strakes:

It isn't obvious if the spokes are a 1/16" or so out, but a 1/16" offset on the strakes would be glaring.

When setting the rivets the expansive force generated by the shank can be enough to distort the T-ring:

My methods are pretty crude, but probably better than the original builders used.

Andrew

Do a lot of practice rivets:

Shorten each rivet by a known amount per step until it looks right. Then shorten all rivets accurately to the same length. That way one achieves consistency:

I chose to make my own fixtures and rivet snaps:

Finished rear wheels:

Andrew

PM sent - Andrew

Surely one first needs to define what is meant by worse, otherwise there is no criteria to judge against?

Andrew

Rolling the gears by hand only tests at one centre to centre distance, which may not be the optimal distance. So the jury is still out! In neither case are the involutes conjugate so there will never be a mainly rolling action, ie, there must be some sliding as well.

Andrew

That can't be right? A speed of 30kph is equivalent to 18.6mph.

Andrew

My maths is usually more than good enough; but I'm stumped as to how electron tunnelling in diodes is applied to boiler design? On another forum it was stated that the analysis of a steam engine governor needed to be done with the z-transform. I wonder if that would help here, especially as the coal is fed in discrete lumps?

Andrew

I normally do that once a year during my annual workshop clean up and oil. I use a small, very fine, oilstone that I inherited from a toolmaker.

Andrew

Done - Andrew

Exactly! It's one reason I continue my build diary on TT but rarely here or on MEM. It takes time and effort to create a build post so I concentrate that effort where I get feedback and, more importantly, useful discussion.

It's strange that the OP only has 3 photos to his name, none of which seem to be visible?

Andrew

Never had a vice move under cutting forces - work yes, but vice no. I can't see any need to put paper under the vice and introduce an unknown variable that may upset the parallelism of the vice to the table.

Andrew

Rest assured that should a "like" button be introduced I wouldn't click it on any of your posts.

Andrew

I use a lot of split mandrels, so it's natural for me to use bolts. It's simpler and quicker for me to drill and tap than it is to turn down and thread. I also find it quicker to use a bolt than a nut and spanner.

Andrew

Jason is correct on the acronym, athough a countersunk screw would work. But the Allen key will be smaller, so you need a smaller gorilla to do it up.

Andrew

That's why I didn't say machine part of the OD in the 4-jaw chuck.

A disc supported only at the centre is a .......... cymbal! Good in a drum kit but not so useful on a lathe. For the spigot I'd make the diameter of the backing surface about half the OD of the part, say around 50mm barstock. Same for the washer at the front, and I'd use a SHCS instead of a nut. Making the diameter of the driving surfaces a good proportion of the part OD means that the part is less likely to slip when taking proper cuts to avoid work hardening.

Andrew