Module alignment: My favourite

Achieving good module alignment is actually a pretty interesting process. Even when it goes wrong you learn a lot quite quickly. The basics are that you want the modules to align as best as possible along the join and more specifically that the track is in alignment both visibly and within the range of your measuring equipment. If you can see a misalignment you’ll need to start again or fettle until the rails or trackbed are suitably located. What follows is from experience gained joining both raw benchwork and fully tracked modules.


7/8″ female and male pattern maker’s dowels ready to be installed

In the past I’ve used corresponding wooden wedges to  set vertical and horizontal alignment  but that rarely allows for easy scenic treatment unless the middle  triangular piece is full width which it couldn’t be on Scenic as the switches fall too near the baseboard edges. That system also relies a little too much on gravity but they are easy to make. On the last few sets of modules I’ve opted for home made pattern maker’s dowels which seems to be a traditional  manner of mating adjacent  modules in the UK.

The dowels I made are 7/8″ diameter and quite similar in overall appearance to the Station Roads product regularly advertised inside the cover of Model Railway Journal. The first sets I made were done on my trusty little Taig lathe but I’ve since added a much bigger Compact8 Clone that really moves metal. I’ve also switched to cold rolled 1018 from 12L14 because, well, I’m cheap, and I’m told it has a little better rust resistance. The three mounting holes are drilled on the mill using coordinates to lay them out on the pitch circle diameter. Coordinates and relevant formulas for laying out holes can be found in most shop references.

Section through pattern maker’s dowel set and baseboard end profile

Section through pattern maker's dowels and baseboard end profiles

I went for a small amount of clearance (.002″) between matched pairs as this seemed to be what commercial offerings are spec’d with but I’m not yet certain I will continue with that amount in every situation. Certainly you don’t want slop but I’m beginning to wonder if one tight fitting dowel and one looser, say with .005″ clearance, would not be a better path to follow. The thinking is that this might  allow modules stored in locations with significantly different humidity levels to join without fuss and still be “rotated” into reasonably tight alignment. A little slack would also allow for more tolerance should the dowels be nosed up or down though that isn’t in itself a good reason to make sloppy work.

With dowels in hand the next step is figuring out how to locate the recesses into the module end plates. In general you can’t just drill through one and into the other the way you could if you were locating wood doweling so some other method of locating needs to be used if good fits are to be had. I made a three piece drilling jig out of 3/4″ plywood to help keep the cordless drill and Forstner bit in place. Drilled on a drill press and aligned with appropriate dowels whatever precision the jig has is built into it when you screw all of the bits together, hopefully with plenty of clamping. Were I smart I would have built it out of two pieces on my milling machine, not having adequate travel stop me in this instance.  My jig is a bit on the sloppy side but not so much that I’m in a hurry to take it apart and start over. There are a couple of reasons for this: for starters I’m working on an aluminium jig to replace the current wooden model, and two, the holes can be scraped to a working fit in a short amount of time.


Left to right: pilot drill, 1/4-20NC clearance drill, Forstner bit, drill jig, C clamps

The bottom piece of the jig gets pressed tight against the bottom of the module end plate and once centred the jig gets clamped with a deep throated C clamp. Drilling is with firm pressure trying as best as possible to keep things square and neat as the drill progress through the jig and into the end plate. I gauged the depth by feel drilling both holes before removing the jig to inspect. Usually I’ve gotten to within .020″ of final depth after which the hole is finished free hand without the jig. My procedure thus far has been to sort out matched pairs and locate the females on one module and once they are attached to sort out the corresponding male dowels. It is important to keep the dowels square and flush to the module end pieces and one way to do this is to affix the female pieces temporarily to the end plates with gel CA and then place three 1/2″ flat round magnets around the perimeter to hold the dowel true and without rock. A bit of masking tape helps to hold the magnets “in”.


Gel CA as a leveling medium

Once the female dowels cured they were drilled and screwed to the baseboards with 3/4″  No.5 screws. That done every effort was made to ensure that both modules were level to one another in a bid to prevent registration errors. The male dowels were then test fit and the modules tested for mating. Usually there is enough slack between the holes and the dowel pieces that everything lines up well enough but on one occasion I had to scrape the opening down to be able to raise the roadbed up. This was accomplished with a No.11 knife blade and the gaps at the top of the dowel were filled with tinfoil and the aforementioned gel CA. It’s actually a pretty good idea to make a tinfoil sheath on each dowel as a sort of fail-safe in the event that things don’t work out first time round. I’ve tested this out and it makes retrieving ill-placed dowels much easier.


Dowel packed and surrounded with tinfoil

With a bit of luck and some messing about the modules should go together without to much fuss. What ever you do you don’t want the male dowels to nose towards or away from one another. with .002″ clearance you can run into problems quite quickly. Once things are thought to be true the real work of affixing the first male dowel can begin. By doing one at a time you minimize the chances of jamming the modules together due to misalignment. I use gel CA as on the female sides but rather than magnets I make sure the back of the dowel face is packed with tinfoil and gel CA until just flush and then mate the modules together to ensure the female dowel keeps the male true. Once the CA has kicked off the modules are broken and the screw holes drilled and screwed carefully to avoid disturbing the dowel’s position. If things look good the second dowel is dry fit and the modules again cinched up, repeating with gel CA once everything checks out. If after all is said and done the modules perform satisfactorily the final screws can be added. By torquing the screws minor issues of alignment can be dialed out but one has to move slowly and deliberately, often in the order of eighth or sixteenth turns.

It is also worth mentioning that clearance holes for 1/4-20NC were drilled once things were settled. I’ve heard and read that it is handy to standardize on one type of hardware for display layouts. Not being able to think of a reason why 1/4-20NC would be unsuitable I went with what I had to hand.


Male dowel packed out with tinfoil and temporarily position with gel CA

While all of this looms large in written form the process is actually fairly straight forward.

If I had a checklist it would be this…

1. Drill as straight and true as facilities allow. Use a jig.

2. Make life easy and ensure the dowels on the first module are set up straight. The second module can only be as good as the first.  Use magnets if need be to hold them straight and flush with the end of the module. Pack the dowels on the first module with tin foil like a peanut butter cup so that they stay centred in the hole.

3. Give the gel CA time to set up. Before screwing through the dowels the CA needs to be hard enough to provide a firm and stable base for the dowel.

4. Carefully fasten the dowels screwing into pre-drilled holes to avoid rocking the dowel.

5.When attaching dowels to the second module place both in their respective sockets but only glue one at a time. If things go sideways at least one dowel is correctly aligned.

6. Clamp and let the gel CA dry thoroughly before unclamping and repeating for the second dowel.

7. Don’t be scared to scrape and pack the hole to achieve correct alignment on the final hole.

8. Unbolt and double-check final alignment. If the first module’s dowels are true those on the second module should follow suit.

Hopefully this post can be of some use down the road – I haven’t found a lot of pattern making books that deal with doweling in a way easily transferred to the model railway world. I’ll update again once the new aluminium jig moves beyond the mock up stage.