Jig for drilling crankpin hole

Julian Roberts
Posts: 778
Joined: Sat Jan 09, 2010 11:33 pm

Jig for drilling crankpin hole

Postby Julian Roberts » Mon Dec 02, 2019 9:07 pm

I've got some new Gibson wheels with dimples only. They aren't available with a hole. All that's required is to drill the hole vertically. Hah! - not so terribly easy to get it really accurately vertical.

I'm pretty sure I saw here a jig for doing this that may have been commercially available, with several holes for various crankpin throws. But I can't find anything about it using the Search facility nor see a relevant subject heading in the Index. It will be buried somewhere buried in various build threads. So I'm wondering if anyone recalls this item or further information?

Meanwhile here is the wheel (1 of 4) and my home brewed jig I made for a similar task a few years ago, that I will copy with longer throw if nothing better is available to buy.
20191130_222104-1.jpg

20191202_123150-1.jpg

20191202_182522.jpg

User avatar
Steve Carter
Posts: 339
Joined: Tue Nov 11, 2008 6:51 pm

Re: Jig for drilling crankpin hole

Postby Steve Carter » Mon Dec 02, 2019 10:27 pm

Hi Julian

Have a look at this on the CLAG website http://www.clag.org.uk/crankpin-drilling.html

I’ve used the jig and vertical drill method to drill the crank pin holes in some AG wheels with dimples. It worked ok :thumb

Good luck

Steve
Steve Carter

User avatar
jon price
Posts: 480
Joined: Mon Jun 07, 2010 2:34 pm

Re: Jig for drilling crankpin hole

Postby jon price » Mon Dec 02, 2019 10:47 pm

"Drill both points 0.75mm, then open out one to 3.1mm or 1/8". If possible, do this in a drill press to ensure the holes are vertical and parallel, otherwise do what you can by hand." is the CLAG advice for making a jig if you don't have machines. Which doesn't guarantee vertical crankpins, just that they will all slope at the same angle in the same direction.

User avatar
grovenor-2685
Posts: 3175
Joined: Sun Jun 29, 2008 8:02 pm

Re: Jig for drilling crankpin hole

Postby grovenor-2685 » Mon Dec 02, 2019 11:20 pm

Julian Roberts wrote:I've got some new Gibson wheels with dimples only. They aren't available with a hole. All that's required is to drill the hole vertically. Hah! - not so terribly easy to get it really accurately vertical.

I'm pretty sure I saw here a jig for doing this that may have been commercially available, with several holes for various crankpin throws. But I can't find anything about it using the Search facility nor see a relevant subject heading in the Index.

In Allan Goodwillie's magnum opus, see https://www.scalefour.org/forum/viewtopic.php?f=39&t=666#p3534
Rgds

David Knight
Posts: 631
Joined: Sun Jul 20, 2008 6:02 pm

Re: Jig for drilling crankpin hole

Postby David Knight » Tue Dec 03, 2019 2:18 am

FWIW another variation on the same theme can be found here; viewtopic.php?f=20&t=2019&start=50#p18358

Cheers,

David

User avatar
Le Corbusier
Posts: 1374
Joined: Wed Feb 11, 2015 3:39 pm

Re: Jig for drilling crankpin hole

Postby Le Corbusier » Tue Dec 03, 2019 7:56 am

jon price wrote:Which doesn't guarantee vertical crankpins, just that they will all slope at the same angle in the same direction.


As Kieth has mentioned, Allan's Crankpin jig will allow you to tweak each crankpin with a pair of pliers to ensure that they all sit vertical ... so achieving the same position and the same angle slope could work?

Crankpin Jig - 6.jpg
Crankpin Jig - 5.jpg
Tim Lee

User avatar
Jol Wilkinson
Posts: 788
Joined: Mon Jul 21, 2008 7:39 pm

Re: Jig for drilling crankpin hole

Postby Jol Wilkinson » Tue Dec 03, 2019 9:11 am

Drilling soft materials such as plastic normally calls for a drill with a smaller rake than standard drills. I wonder whether the small diameter drills we use are likely to wander off centre while drilling plastic, even with a jig in use? Drill speed may also have an impact on the accuracy of the drills alignment while cutting, a slow speed and feed rate would seem to be optimum.

I use a 3.2mm shank drill with short flutes, mounted in the milling attachment on a Unimat. I mount the wheel on a dummy, light push fit, axle which is held in the Unimat machine vice bolted to the cross slide. Although I don't use a jig, once set up, each wheel can be drilled consistently.

Having said that, I haven't done any for some time, managing to get Sharman Wheels (when they were still available) for my current small stash of kits.

Julian Roberts
Posts: 778
Joined: Sat Jan 09, 2010 11:33 pm

Re: Jig for drilling crankpin hole

Postby Julian Roberts » Tue Dec 03, 2019 11:10 am

Very many thanks all. :thumb

User avatar
Tim V
Posts: 2265
Joined: Tue Jul 29, 2008 4:40 pm

Re: Jig for drilling crankpin hole

Postby Tim V » Tue Dec 03, 2019 11:17 am

I think I covered this in my workshop thread, but I consider that it's important to drill from the back of the wheel - thus ignoring the countersink. That way the drill will follow the direction you intend, rather than what it wants to do!
Tim V
Scalefour News Editor

User avatar
David Thorpe
Posts: 831
Joined: Tue Oct 21, 2008 11:13 pm

Re: Jig for drilling crankpin hole

Postby David Thorpe » Tue Dec 03, 2019 11:36 am

I'm not at all sure that if you don't have the skill to drill the hole you've got the skill to make one of these jigs. As I've probably got neither I wonder if the Society might like to commision and sell the Goodwillie jig, either as a kit or Ready-to-Drill? It does seem an Extremely Useful Item.

DT

User avatar
Le Corbusier
Posts: 1374
Joined: Wed Feb 11, 2015 3:39 pm

Re: Jig for drilling crankpin hole

Postby Le Corbusier » Tue Dec 03, 2019 11:46 am

David Thorpe wrote:I'm not at all sure that if you don't have the skill to drill the hole you've got the skill to make one of these jigs. As I've probably got neither I wonder if the Society might like to commision and sell the Goodwillie jig, either as a kit or Ready-to-Drill? It does seem an Extremely Useful Item.

DT


I didn't find the jig too difficult to make ... which I hasten to add is not a way of blowing my own trumpet. The channel simply slides into the box section and the fabrication is very little different to soldering up a simple un sprung/uncompensated chassis. :thumb

Crankpinjig.jpg
Crankpinjig.jpg (31.02 KiB) Viewed 521 times
Tim Lee

best33
Posts: 18
Joined: Thu May 12, 2011 12:05 pm

Re: Jig for drilling crankpin hole

Postby best33 » Tue Dec 03, 2019 12:52 pm

The important point with this is that all the holes have to be the in the same radial position relative to the axle and at the same angle (ideally parallel to the axle).

If you make a jig with an error, but it results in all the drilled holes being the same on every wheel then it should work OK. There is quite a lot of slop in Gibson Crankpins between the bore in the bush and the outside diameter of the thread of the bolt which can also introduce variability.

The crank pin nut should be tight to the end of the bush and should not rest on the coupling rod. Often the bushes are too short so you can either thin the rods slightly or find a longer bush. If the nut rests on the coupling rod you run the risk of either locking the wheels up or the nuts undoing themselves depending on the direction of running.

The Gibson bushes have a large flat flange on the wheel hub side so getting this to sit down flat is also important. Sometimes there can be a bit of swarf which prevents this.

Personally I prefer the Ultrascale system where the crank pin bush is located in a pocket on the wheel which sets the correct position and the bolt passes through the middle and the nut clamps the end of the bush. In this case if the bolt is slightly out of true it doesn't matter.

User avatar
Will L
Posts: 1665
Joined: Sun Jul 20, 2008 3:54 pm

Re: Jig for drilling crankpin hole

Postby Will L » Tue Dec 03, 2019 9:49 pm

Yes we have been past the need to drill the crankpin holes in GW wheels problem a number of times. I got the problem nearly 9 years ago as described in this post, which I give for completeness rather than anything else. I seem to remember there was talk of the society producing a variable jig at the time but nothing came of it. I had to reuse the simple jig described in the post recently as I found the the GER/LNER F7 I'm building had crankpin hole free wheels too, fortunately with the same crank pin throw. Both times (that's 10 wheels) it's worked well for me in my machine tool free zone, suggesting we need not overcomplicate the solution.

Tim V wrote:I think I covered this in my workshop thread, but I consider that it's important to drill from the back of the wheel - thus ignoring the countersink. That way the drill will follow the direction you intend, rather than what it wants to do!


But surely if you drill from the back and the drill does wander a bit, that they wont exit the wheel face in the same place on each wheel giving you a (subtly) different crank pin throw on each wheel? Potential result "unexplained" tight spots? While if you drill from the front face the jig should ensure the crank pins exits the face of the wheel at the same distance from the axle centre no matter exactly where they go in on the others side.

User avatar
Le Corbusier
Posts: 1374
Joined: Wed Feb 11, 2015 3:39 pm

Re: Jig for drilling crankpin hole

Postby Le Corbusier » Tue Dec 03, 2019 11:22 pm

Will L wrote:But surely if you drill from the back and the drill does wander a bit, that they wont exit the wheel face in the same place on each wheel giving you a (subtly) different crank pin throw on each wheel? Potential result "unexplained" tight spots? While if you drill from the front face the jig should ensure the crank pins exits the face of the wheel at the same distance from the axle centre no matter exactly where they go in on the others side.


And then you can use Allan's jig to gently straighten them to vertical.... and bingo :thumb
Tim Lee

User avatar
Tim V
Posts: 2265
Joined: Tue Jul 29, 2008 4:40 pm

Re: Jig for drilling crankpin hole

Postby Tim V » Wed Dec 04, 2019 11:25 am

Will L wrote:
Tim V wrote:I think I covered this in my workshop thread, but I consider that it's important to drill from the back of the wheel - thus ignoring the countersink. That way the drill will follow the direction you intend, rather than what it wants to do!


But surely if you drill from the back and the drill does wander a bit, that they wont exit the wheel face in the same place on each wheel giving you a (subtly) different crank pin throw on each wheel? Potential result "unexplained" tight spots? While if you drill from the front face the jig should ensure the crank pins exits the face of the wheel at the same distance from the axle centre no matter exactly where they go in on the others side.

The whole point is to make sure the drill cannot wander, drilling onto a flat surface should mean the drill following its own path. You cannot know that the countersink on the front of the wheel is consistent across all the wheels, but you do know the back is flat.
Tim V
Scalefour News Editor

davebradwell
Posts: 119
Joined: Fri Jan 18, 2019 3:48 pm

Re: Jig for drilling crankpin hole

Postby davebradwell » Wed Dec 04, 2019 11:59 am

Can we just agree that, well it's not sensible to drill from the back of the wheel if all crank throws are to have a chance of being similar. If the drill comes out off-piste then straightening it is just going to produce a straight crankpin in the wrong place. A small pip in soft abs isn't going to influence any drill that's just travelled 2mm. through the same.

Further, with Julian's soldered up jig, or any other for that matter, the drill must be a very close fit in the tube and therefore should have cut the hole itself. Finding a piece of handy tube that seems to fit will probably allow a few thou' unnecessary error and all these little numbers add up.

Nice to hear some sound stuff from best33 and particularly his suggestion to use Ultrascale crankpins although you will have a wait if you don't hold a stock. It's the same logic as above - the hole in the front of the wheel is nearer to the coupling rod so less chance of going astray.

Finally, I get the impression that many folk in this hobby based on making things have no proper means of drilling a hole. This seems a fundamental operation as so many parts have at least one. A drilling machine is the cheapest and smallest gadget and much safer than a pistol drill as the job can be clamped down. I bought mine not long after I had a house to put it in. Just the thing for Christmas! I will add this isn't meant as criticism, more a surprising reflection on the changed world we live in where students leave school never having used a file or drilled a hole and need instructions with their toothpicks.

DaveB

User avatar
Tim V
Posts: 2265
Joined: Tue Jul 29, 2008 4:40 pm

Re: Jig for drilling crankpin hole

Postby Tim V » Wed Dec 04, 2019 12:36 pm

Actually no.

My workbench thread covers the jig I made viewtopic.php?f=105&t=913&start=175
Tim V
Scalefour News Editor

Philip Hall
Posts: 1305
Joined: Mon Aug 10, 2009 7:49 pm

Re: Jig for drilling crankpin hole

Postby Philip Hall » Wed Dec 04, 2019 12:46 pm

Dave, I'm with you here. I think it's much easier to see what's happening if you drill from the front of the wheel, it's easier to have the wheel flat on the drilling table, and if the drill is running at a reasonable speed and you take it gently the drill ought not to follow the dimple, after all it's soft plastic. I've never had any trouble when drilling these wheels, even without a jig.

But, I always use a small pillar drill. A long time ago I bought a Proxxon TBM220 - which turned out to be amazingly true and well made - and although it doesn't get a lot of use, for things like this it's a must. I sometimes use a simple jig made from a thick strip of brass (like the CLAG one) if I want to change the crank throw (eg for a 45XX where the dimpled throw is too small, or a LSWR 700 where it's too great). I have the minimum amount of the drill protruding from the chuck which stops it flexing too much. I drop the drill into the dimple and 'centre' the wheel under it, then bring the drill up again and turn it on. Then with a reasonable speed I start the hole but allow the drill to start cutting before I put any real pressure on it. That way, I figure the drill will not allow the dimple to dictate the location to any degree.

Now I know that drills can wander, but I've never had a problem with crank throws being inconsistent, but maybe I've been lucky. Increasingly these days I find I like the engineering precision that comes with machine tools, even though my skills are limited. I realise that I am fortunate to have a few of these tools and that they are not available to everyone, but a small pillar drill like the Proxxon is not that expensive really and so useful.

Philip

User avatar
Tim V
Posts: 2265
Joined: Tue Jul 29, 2008 4:40 pm

Re: Jig for drilling crankpin hole

Postby Tim V » Wed Dec 04, 2019 12:56 pm

Agree with you Phillip about the need for a precision vertical drill.

If there is any doubt about one's ability to drill a vertical hole through the wheel - don't do it. All this talk of worrying that the hole 'might' not be vertical. If that is the case, clearly something is wrong, you need to examine the method you are using.

I know with certainty that my method produces the correct result. Therefore that is the method I recommend, because it works reliably.

I am not forcing it on other modellers, merely saying it works for me.
Tim V
Scalefour News Editor

Philip Hall
Posts: 1305
Joined: Mon Aug 10, 2009 7:49 pm

Re: Jig for drilling crankpin hole

Postby Philip Hall » Wed Dec 04, 2019 1:13 pm

Tim,

Looking at your workbench thread, it looks to me as if the wheel has been inserted into your turned jig face down, and when the jig is turned the other way around for the wheel to be drilled through the jig, the wheel is actually being drilled from the front. Can you clarify please? Or tell me I'm having another senior moment!

Philip

User avatar
Tim V
Posts: 2265
Joined: Tue Jul 29, 2008 4:40 pm

Re: Jig for drilling crankpin hole

Postby Tim V » Wed Dec 04, 2019 1:32 pm

Illustrative purposes only!
Tim V
Scalefour News Editor

User avatar
Le Corbusier
Posts: 1374
Joined: Wed Feb 11, 2015 3:39 pm

Re: Jig for drilling crankpin hole

Postby Le Corbusier » Wed Dec 04, 2019 1:44 pm

Tim V wrote:Agree with you Phillip about the need for a precision vertical drill.

If there is any doubt about one's ability to drill a vertical hole through the wheel - don't do it. All this talk of worrying that the hole 'might' not be vertical. If that is the case, clearly something is wrong, you need to examine the method you are using.

I know with certainty that my method produces the correct result. Therefore that is the method I recommend, because it works reliably.

I am not forcing it on other modellers, merely saying it works for me.


I certainly defer to more experienced and better modellers than me.

But what I will say is that correction does seem to work.

For my Barney I had Gibson wheels without pre-drilled crankpin holes. When i fitted the crankpins (a few years ago now) I failed to ask advice and simply used a hand held archimedes drill to drill a pilot hole through the dimple from the front and then screwed in the pin from the back. The positioning of the pins was pretty good, but the angles were certainly off. I straightened them by eye and managed to get things running ok by means of enlarging the holes on the rods coupled to the built in slop in the Gibson bushes.

However, I have subsequently used Allan's jig to check both the position and verticality of the pins. The positioning is pretty good, and by gentle tweaking I have adjusted the angles such that i have got them to house down cleanly into the jig with a drop fit. Putting the whole thing back together, the motion is noticeably smoother with no apparent binding. So all might not be lost if you don't have a pillar drill?
Tim Lee

User avatar
Tim V
Posts: 2265
Joined: Tue Jul 29, 2008 4:40 pm

Re: Jig for drilling crankpin hole

Postby Tim V » Wed Dec 04, 2019 2:14 pm

But it's surely better to get it right first time.

So many modellers give up because they can't get it right. A great pity.

We should be pressing for decent wheels that don't need drilling. Wheels that are round and square to the axles. Wheels that self-quarter.

Oh well we can all dream ...
Tim V
Scalefour News Editor

User avatar
David Thorpe
Posts: 831
Joined: Tue Oct 21, 2008 11:13 pm

Re: Jig for drilling crankpin hole

Postby David Thorpe » Wed Dec 04, 2019 2:26 pm

Having looked rather more carefully at Allan's jig, it strikes me that it may not be as uselul as i had initially thought because I've realised that it doesn't actually offer any assistance in drilling the hole through the wheel, which is, I think, what Julian (and me for that matter) would like. As far as I can see, Allan's jig is used after the hole has been drilled through the wheel and does not resolve the problem of drilling a staright vertical hole in the first place.

DT

User avatar
Le Corbusier
Posts: 1374
Joined: Wed Feb 11, 2015 3:39 pm

Re: Jig for drilling crankpin hole

Postby Le Corbusier » Wed Dec 04, 2019 2:42 pm

David Thorpe wrote:Having looked rather more carefully at Allan's jig, it strikes me that it may not be as uselul as i had initially thought because I've realised that it doesn't actually offer any assistance in drilling the hole through the wheel, which is, I think, what Julian (and me for that matter) would like. As far as I can see, Allan's jig is used after the hole has been drilled through the wheel and does not resolve the problem of drilling a staright vertical hole in the first place.

DT


.... Allan's jig as far as I am aware is only to check that the positions match across all wheels and to allow tweaking to ensure that the pins sit vertical to the wheels. A simple disc with centre bush and soldered in axle rod, plus guide hole(s) for the pin position(s) should allow accurate location of holes to be drilled relative to the centre of the wheel ...

Much prefer the idea of a pillar drill ... but if needs must, this does seem to work.
Tim Lee


Return to “Steam Locomotives”

Who is online

Users browsing this forum: No registered users and 2 guests