Steph Dale
Western Thunderer
Col,
That's because they are Laurie Griffin's
Do not pass Go, do not collect £200....
Steph
That's because they are Laurie Griffin's
Do not pass Go, do not collect £200....
Steph
Crank axles for split axles
- Thread starter Steph Dale
- Start date
Stevesopwith
Western Thunderer
Please may I join Graham in the Crankpin Bush tapping class.
Eastsidepilot
Western Thunderer
Col,
That's because they are Laurie Griffin's
Do not pass Go, do not collect £200....
Steph
doh........It's been one of those days mate
Col.
Steph Dale
Western Thunderer
This is perhaps where it starts to get tricky!
The next step is to drill in the end of the axle with a 2mm dia. drill. The aim is to drill deep enough that the end of the drilled hole is between the cheeks of the crank. The position of the end of the hole then needs cross drilling in a convenient size - I used the first drill I laid my hands on, which was 0.7mm dia. The 2mm dia. hole will then take a short length of 2mm GRP rod, which will later form the core of the insulation in the axle. This picture shows the depth of the hole drilled, by the permanent pen mark on the rod. You'll note that at this stage the rods are over-length and that the ends of the rods have been shaped to make them easy to insert:
The two rods are then cut off to length, this is roughly 3mm shorter than the depth of the 2mm dia hole. As you can see, the rods are prepared individually so need marking for which end of the axle they go in. No permanent pen on the rods when ready to install, previous experience has demonstrated that permanent pen ink and epoxy adhesives are not best buddies!
The rods can then be keyed up with an old file before mixing a quantity (don't skimp!) of DevCon 2-ton, which is then wodged into the ends of the axle, the GRP rods are then smeared in the epoxy and stuffed in to the drilled holes each end with a cocktail stick. As you do this, excess glue will squirt out of the 0.7mm hole. I managed to do both at the same time and then left the axle with the two 0.7mm holes uppermost for the adhesive to cure.
With the adhesive now through initial cure, I thought I'd show you how this crank axle would fit into a 'normal' finescale chassis. This is the one from the G6 before its imminent disassembly and you can see that with some suitably thinned bearings there's no problem getting it to fit. In fact, in finescale, it can often be the area around the slidebars that ends up as the pinch point, but I guess that's a digression...
I'm off for another rummage through the G6 box and have a look at making up a few more components/sub-assemblies. Or perhaps tap a crankpin bush or two and take some more piccies.
Steph
The next step is to drill in the end of the axle with a 2mm dia. drill. The aim is to drill deep enough that the end of the drilled hole is between the cheeks of the crank. The position of the end of the hole then needs cross drilling in a convenient size - I used the first drill I laid my hands on, which was 0.7mm dia. The 2mm dia. hole will then take a short length of 2mm GRP rod, which will later form the core of the insulation in the axle. This picture shows the depth of the hole drilled, by the permanent pen mark on the rod. You'll note that at this stage the rods are over-length and that the ends of the rods have been shaped to make them easy to insert:
The two rods are then cut off to length, this is roughly 3mm shorter than the depth of the 2mm dia hole. As you can see, the rods are prepared individually so need marking for which end of the axle they go in. No permanent pen on the rods when ready to install, previous experience has demonstrated that permanent pen ink and epoxy adhesives are not best buddies!
The rods can then be keyed up with an old file before mixing a quantity (don't skimp!) of DevCon 2-ton, which is then wodged into the ends of the axle, the GRP rods are then smeared in the epoxy and stuffed in to the drilled holes each end with a cocktail stick. As you do this, excess glue will squirt out of the 0.7mm hole. I managed to do both at the same time and then left the axle with the two 0.7mm holes uppermost for the adhesive to cure.
With the adhesive now through initial cure, I thought I'd show you how this crank axle would fit into a 'normal' finescale chassis. This is the one from the G6 before its imminent disassembly and you can see that with some suitably thinned bearings there's no problem getting it to fit. In fact, in finescale, it can often be the area around the slidebars that ends up as the pinch point, but I guess that's a digression...
I'm off for another rummage through the G6 box and have a look at making up a few more components/sub-assemblies. Or perhaps tap a crankpin bush or two and take some more piccies.
Steph
Dog Star
Western Thunderer
Hi Steph,
I guess that the GRP insert is shorter than the depth of the hole to enable the 6BA socvket screw to be inserted... how do you arrive at the figure of 3mm as the different in length?
When wodging the adhesive, how do you prevent to the stuff from gunging the internal thread of the axle?
thanks for the pikkies, Graham
I guess that the GRP insert is shorter than the depth of the hole to enable the 6BA socvket screw to be inserted... how do you arrive at the figure of 3mm as the different in length?
When wodging the adhesive, how do you prevent to the stuff from gunging the internal thread of the axle?
thanks for the pikkies, Graham
Steph Dale
Western Thunderer
Graham,
Correct; you remember back in post #9 I shortened the screws? Well this means that the screws don't project further into the axle than the shoulder. The 3mm length quoted above is the length of the square section. So, shortening the GRP rods by 3mm means that the screw and rod only just meet. I'm still expecting to have to carry out some level of adjustment in this area (which will probably be in the next session), but it won't be as bad as it could be. It also means I've got the greatest length of GRP rod in the axle that's possible, which should help with the strength of the completed assembly.
In general I'm not adverse to the adhesive gunging up the thread. Once the adhesive is cured I'll run a 6BA plug tap down the end of the axle.
Steph
Steph Dale
Western Thunderer
Steph Dale
Western Thunderer
And so to tonight's (short) installment, subtitled 'don't do it this way'...:
Here's a shot of the crank after cross drilling the cranks and axle. The intention was to pin the GRP rod in place, but with a further two broken drills now incorporated in the construction of the crankaxle I can fairly say two things:
1. It's not going to come apart.
2. It's starting to get a bit irritating.
So, armed with what I know now I'd be tackling this slightly differently. The original GRP insulated axles don't make use of any cross pins - they don't need to as they have the wonderful idea (not mine) of cross drilling the axle in a few places before the rod is glued in place. This (much easier) process throws up a burr on the inside of the axle which the GRP rod and epoxy can happily latch on to, so that's what I'd be doing instead of trying to drill some awful deep holes with fine drills through a mixture of nickel-silver, steel, epoxy resin and GRP. On reflection there was no way that was going to end well!
Anyway, here's the axle cross-drilled 0.5mm and with 0.45mm half-hard brass (handrail) wire epoxied in the resulting holes. Some care is required here as three of the four holes are blind (and two of those have broken drills in their bottoms), so the epoxy needs plenty to be applied to pin, orifice and thereabouts, the pin can then be 'pumped' in the hole to exclude any air:
Next time I'll start cleaning up the threads and pins and make a first couple of cuts of the axle. This is the point at which nerves will be required!
Steph
Here's a shot of the crank after cross drilling the cranks and axle. The intention was to pin the GRP rod in place, but with a further two broken drills now incorporated in the construction of the crankaxle I can fairly say two things:
1. It's not going to come apart.
2. It's starting to get a bit irritating.
So, armed with what I know now I'd be tackling this slightly differently. The original GRP insulated axles don't make use of any cross pins - they don't need to as they have the wonderful idea (not mine) of cross drilling the axle in a few places before the rod is glued in place. This (much easier) process throws up a burr on the inside of the axle which the GRP rod and epoxy can happily latch on to, so that's what I'd be doing instead of trying to drill some awful deep holes with fine drills through a mixture of nickel-silver, steel, epoxy resin and GRP. On reflection there was no way that was going to end well!
Anyway, here's the axle cross-drilled 0.5mm and with 0.45mm half-hard brass (handrail) wire epoxied in the resulting holes. Some care is required here as three of the four holes are blind (and two of those have broken drills in their bottoms), so the epoxy needs plenty to be applied to pin, orifice and thereabouts, the pin can then be 'pumped' in the hole to exclude any air:
Next time I'll start cleaning up the threads and pins and make a first couple of cuts of the axle. This is the point at which nerves will be required!
Steph
Steph Dale
Western Thunderer
Nearly there now.
This is, I think pretty much where we left it. The pins have been trimmed flush, filed and polished back to the surface.
I then ran a 2.3mm drill down the ends of the axle as far as the GRP rod, to remove excess adhesive, before following up with a 6BA plug tap. Mine is very slightly modified from as purchased as the bottom face of the tap has been ground flat on a grindwheel in my Dremel. This is the one I usually use for clearing threads when making split axles using GRP rod. You may be lucky and get hold of a proper 6BA third/plug tap, otherwise you could grind it to match mine!
Threads cleaned, screws test fitted, successfully:
And so cut the cranks. I support the crank like this:
Using a no.0 piercing saw blade I then worked through the axle next to the inner crank web:
Followed by the outside one, releasing a small section of 3/16" axle, with a 2mm GRP rod down its middle:
And repeat for the other side. I then shoved the axle in a spare chuck to make it easier to hold when cleaning up the inside faces of the crank webs. For this job I use a flat 'warding file'. Probably second cut.
Which gets us to this. If this was a normal crank axle this'd be pretty good, but we've still got to sort the insulation, so more in a moment or two:
Steph
This is, I think pretty much where we left it. The pins have been trimmed flush, filed and polished back to the surface.
I then ran a 2.3mm drill down the ends of the axle as far as the GRP rod, to remove excess adhesive, before following up with a 6BA plug tap. Mine is very slightly modified from as purchased as the bottom face of the tap has been ground flat on a grindwheel in my Dremel. This is the one I usually use for clearing threads when making split axles using GRP rod. You may be lucky and get hold of a proper 6BA third/plug tap, otherwise you could grind it to match mine!
Threads cleaned, screws test fitted, successfully:
And so cut the cranks. I support the crank like this:
Using a no.0 piercing saw blade I then worked through the axle next to the inner crank web:
Followed by the outside one, releasing a small section of 3/16" axle, with a 2mm GRP rod down its middle:
And repeat for the other side. I then shoved the axle in a spare chuck to make it easier to hold when cleaning up the inside faces of the crank webs. For this job I use a flat 'warding file'. Probably second cut.
Which gets us to this. If this was a normal crank axle this'd be pretty good, but we've still got to sort the insulation, so more in a moment or two:
Steph
Steph Dale
Western Thunderer
The insulation basically involves cutting through the axle down to the GRP rod, so forming an insulation break. Again, I used a chuck to support the axle as I carefully worked it through with a piercing saw blade (still a no.0). I cut this under very bright light so I can see when the steel is cut through and keep a magnifying glass and multimeter handy. With use of saw, bright light, eyesight and a quick test with the 'meter, the first insulating cut is completed and can be seen here on the stub axle next to the chuck:
And repeat for the other stub axle. This provides us with a crank axle where the valvegear can be built as a single unit. In my case that would be part of the frames as I tend to insulate for split axles around the axleboxes, rather than electrically splitting the frames. The latter makes fitting things like inside motion and brakegear a little trickier than I'm comfortable with. So here's the axle fully insulated after final testing with a 'meter:
And the last job for this evening was to grab the DevCon 2-ton and fill the two grooves formed as insulation. The trick with this is the same as I advocate for split axles. I use the relatively low viscosity of the adhesive and put a decent sized blob on the top of the axle, gravity will then do the rest; pulling the adhesive into the groove (I'm sure capillary action helps too) and expelling any air bubbles out the top of the joint:
So that just leaves me to wait until the epoxy has cured, trim up the excess adhesive and give the whole thing a good polish with emery paper to bring it up to it's full glory!
Steph
And repeat for the other stub axle. This provides us with a crank axle where the valvegear can be built as a single unit. In my case that would be part of the frames as I tend to insulate for split axles around the axleboxes, rather than electrically splitting the frames. The latter makes fitting things like inside motion and brakegear a little trickier than I'm comfortable with. So here's the axle fully insulated after final testing with a 'meter:
And the last job for this evening was to grab the DevCon 2-ton and fill the two grooves formed as insulation. The trick with this is the same as I advocate for split axles. I use the relatively low viscosity of the adhesive and put a decent sized blob on the top of the axle, gravity will then do the rest; pulling the adhesive into the groove (I'm sure capillary action helps too) and expelling any air bubbles out the top of the joint:
So that just leaves me to wait until the epoxy has cured, trim up the excess adhesive and give the whole thing a good polish with emery paper to bring it up to it's full glory!
Steph
David Taylor
Western Thunderer
Very tidy work, thanks for showing how it's done!
As for plug taps... I grind down broken taps to make them.
As for plug taps... I grind down broken taps to make them.