Hello and a part-built blowfly

[gingerneer]

Hi Lisa

Regarding the cylinders, if there is no alternative to machining them else were the Taig could do it by unmounting the head stock rotating it through 90 degrees and clamping it down on packing about half way along the bed. It then becomes the spindle of a improvised milling machine. The cylinder held with its port face parallel with the lathe bed is clamped to the cross side. The cross slide is them feeding the depth of cut and the saddle gives you the movement across the cutting face, it would be worth rigging up a lead screw and handle to give you a fine feed control rather than the rack feed on the saddle. It would also be work supporting the tailstock end to prevent spring/deflection. The worst of the lumps and bumps and surface on the casting can be ground off. If you do find the casting 'hard' or hard spots in it bung it in a pile of hot charcoal get it hot hot hot then cover the burning coals and leave to cool over night this should soften/temper the casting. Keep the tool sharp and with fine cuts i think it would be possible. I have seen photos and heard about these such lash ups/ workarounds with much large size machines during the war. I also have a Taig and while i have not tried to machine such large pieces on it they are capable machines if you are gentle and take you time with the cuts. For what its worth you will never have a lathe big enough, in my last job i had a Colchester Master and a couple of fly wheels for Burrell traction engines were turned with barely any clearance on the bed.

Will

[Lisa]

Will, thanks for that, it's solidity that's the main issue, as there are some possible methods that could work. On the other hand I may have got the money for a small mill, hopefully; but best not to count chickens before they hatch and all that.

Meanwhile, I'm clamping bits on to see how they look again:

This is actually the left-hand motion bracket, clamped on the right-hand side, as the right-hand bracket still needs rivetting. The rivets so far have just been given a slight squeeze in the vice to hold them, I need to make a snap to get into the tight corner in order to form the heads properly.

[Lisa]

Both of the motion brackets are now at the same stage, just need to finish those rivets off with a decent shape. Meanwhile, I also cut the slidebars to length (well, length plus a bit, as this will help with the little bit of machining they need), as well as what will become the valve spindle forks.


I must have checked and rechecked about four times to be sure I didn't end up with two motion brackets of the same 'hand'.

[joanlluch]

It's amazing that a video game programmer is now making a miniature locomotive. It seems that these activities have nothing in common, but I guess there's a common set of skills that are required. Such as an organized mind capable of visualize hundreds of seemingly non-related individual tiny parts which joined together will form a much complex, functional system!

[Lisa]

Joan, I'd been working with miniature steam for about 15-20 years before I got into game development, so it's probably the other way around.

It was really too hot in the workshop today, but I wanted to do something, as it's been a little while. So I just finished off one of the slidebars; this meant drilling the bolt hole on the cylinder end, and turning the other end down and threading M5. The bar is too big to pass through the headstock, so needed to be centre drilled in the pillar drill, after careful marking. The extra length mentioned previously was so I could make the turned length slightly longer than the plan says, which gives a little more space to work with for a finishing cut without the tailstock centre getting in the way of the tool.
Naturally, at this point I fitted it to the motion bracket, and clamped it in place on the frames for a look:


On a nearby subject, attaching the piston rod to the crosshead. Every loco I've built/worked on/etc in the past has had the piston rod threaded into the crosshead, with a locknut on the thread. According to the Blowfly plans, however, the piston rod is just pushed into a reamed hole, then held in place with a pin press-fitted into the rod and crosshead. I'm tending toward threading the rods in as per usual, rather than doing the pin thing; partly out of habit, but also because in this situation it seems to me that the reciprocal forces on a cross pin could eventually work it loose.
Just wondering on others' thoughts on the two methods.

Meanwhile dad came up while I was writting this, and said the forum's green colour is the best green he's ever seen.

[Roger]

I've threaded my piston rod and used High Temperature Loctite to bond it to the piston. I'm sure there are many satisfactory ways of doing this.
What I would say is that if you're going to do something where the thread controls the concentricity and alignment of the piston, that you use a die holder that fits in the tailstock to make sure it's true. I'd also leave the finishing cut on the piston to be done while holding the piston rod in the chuck. I'd use the 4-jaw and clock it up. It doesn't matter how carefully you make the parts, there will still be a little runout when you thread the parts together.

[uuu]

Ken Swan has words of support for the screw approach:

"After so much trouble with Hielan Lassie whose crosshead pins kept working loose and dropping out so allowing the piston to "machine gun" the front cylinder cover, I decided that all my future engines would have their piston rods screwed into their crossheads with a small taper pin through to prevent them from unscrewing. Unless building an exhibition job I do not think I would consider using the full-size locomotive pratice of fitting the tapered end of the piston rod into a bored tapered hole in the crosshead, the two being drawn together by a flat tapered cotter. The difficulty of making this arrangement worries me less than the problem of getting them apart again. An examination of any full-size crosshead bears witness to the brutality needed in dismantling."

Wilf

[Lisa]

Thanks Wilf and Roger, that's pretty much firmed up my decision to thread it in. Roger, fortunately the piston rod will fit through the headstock bore, which makes finishing the piston to size like that a great deal easier.

Taking advantage of a cool rainy day, I finished off the other slidebar:

Also got to use the new dial test indicator, which fits nicely in the (rarely used) rear toolpost.
Next parts will be the valve spindle forks, the material for which is the bits of slidebar offcuts in picture. Meanwhile I've almost finished cutting the cast iron blanks for the actual crossheads; just been doing a bit at a time while working on the motion brackets and slidebars.

[Lisa]

A rather warm day cooled off nicely in the late afternoon, so I got to work on the valve spindle forks. Both have now been marked out and the cross holes drilled, and one has now had the spindle boss turned, drilled, and tapped.
I figured I'd cut the actual fork out after the turning, to give the chuck plenty of area to grip on.


The cast iron blanks for the crossheads are also now both cut to length, one of the cuts is quite horrendously out of square; but as they're over-length for cleaning up in the lathe it doesn't really matter beyond giving a bit more to machine off the length.

[Jim]

Hi Lisa, It's all looking good and I see you're using one of those diamond tool cutters. I have tipped tooling but I must admit my diamond tool cutter is my favourite, best thing since sliced bread.

Jim

[Lisa]

Jim, they're brilliant little tool holders, unfortunately the 6mm tool height (3mm square tool) version I use for the Taig lathe doesn't appear to be available from the new suppliers.

[Lisa]

A pleasant Sunday afternoon in the workshop saw me finishing one of the valve spindle forks, and the other not far behind it.
A quick shot of the two forks sitting on the plans.


Then the finished one in-place, the second awaiting cutting and filing, and one of the valve spindle blanks.


It seems I have exactly four of the right sized split pins, so hopefully I don't get clumsy and lose one. Still need to make/modify some washers to go between the fork and the split pin.

[Lisa]

Finished off the valve spindle forks this afternoon, though they still need the washers between split pins and forks added:


Next I'll move on to the crossheads.

Meanwhile, regarding this earlier image:


I think this looks considerably more practical:

Once I get all the tools and collets and such to actually use the mill as a mill, anyway. A bit of luck may actually make that sooner than expected; had to redo some tax returns, seems I'm going to get more of a refund than I did at first.

[Roger]

Oct 12, 2016 8:15:20 GMT Lisa said:

Finished off the valve spindle forks this afternoon, though they still need the washers between split pins and forks added:


Next I'll move on to the crossheads.

Meanwhile, regarding this earlier image:


I think this looks considerably more practical:

Once I get all the tools and collets and such to actually use the mill as a mill, anyway. A bit of luck may actually make that sooner than expected; had to redo some tax returns, seems I'm going to get more of a refund than I did at first.

Digital scales it is then! Good old Tax man!

[Lisa]

Oct 12, 2016 10:07:45 GMT Roger said:

Digital scales it is then! Good old Tax man!

Maybe Roger, would certainly be nice. There's a few other things higher up the list first though (such as cutters so I can use the thing in the first place!); will all depend on how much I get.
At the least, a digital readout for the spindle speed would be handy, rather than guesstimating based on the controller position.

[Roger]

Oct 12, 2016 10:36:07 GMT Lisa said:

Oct 12, 2016 10:07:45 GMT Roger said:

Digital scales it is then! Good old Tax man!

Maybe Roger, would certainly be nice. There's a few other things higher up the list first though (such as cutters so I can use the thing in the first place!); will all depend on how much I get.
At the least, a digital readout for the spindle speed would be handy, rather than guesstimating based on the controller position.

I'm surprised at that Lisa, I have no idea what spindle speed mine's using, I judge it entirely on how it's sounding an from what it looks like.

[Lisa]

I have a few tables (one each for milling, drilling, and turning) that have been drawn up and added to over the years with info from various sources (books, machine manuals, magazine articles, advice from others) with the generally recommended cutting speeds for various sizes of job and tool, and type of material. They're getting a bit faded so I should probably redo them, but they're handy for at least a starting point when setting speeds. Thus why I'd like to know the spindle speed; the lathe and drill have set speeds for each pulley, but one doesn't get that with variable electronic speed control.

[Roger]

I've found over the years that the 'ideal' speeds and feeds are often miles out because our machines have radically different stiffnesses to those used to test cutters. It also varies with the number of teeth, Rippers being different yet again. I guess it's useful as a starting point though.

[Deleted]

I agree with Roger...speed/rate of cut tables have no bearing on what our 'home workshop' machines can do, we need to go much slower...

[Jim]

I still have memories of using the Iscar insert cutter for the first time at "as fast as you can go" recommendation from the supplier. The sight of the cutter hurtling towards the 3 jaw chuck at a million miles and hour while smoking hot blue swarf flew in all directions including my beard, left me trembling as I hit the 'kill' switch.
Since then the Isacar cutter has sat in the tool box and my trusty diamond tangential cutter does all the work at whatever speed I feel comfortable with. The same rule applies to the mill.
Jim