Assembly question

I've reached the part of the assembly of my Ormerod 2 when I am to push the large extruder gear sub-assembly into place in the extruder body. It seams to me like an impossible tight fit. I have double checked that I am using the right bearings. I am reluctant to use a hammer to make it fit, and the alternative seems to widen the hole in the extruder body. Any advice on how to do this? Might using a drill be a solution? Other possible tools?

Thankful for any advice.

The bearings should be fiting tightly ,but if you can not get it in i suggest roling a peice of sandpaper araund a 8mm drill and lightly sand the holes .check regurarly if they fit. while you have fillament in the extruder gear should not be able to fall out.

Thanks for the advice! A few rounds with sandpaper on a 8 mm drill did the trick.

You will find when you start printing that the exact size of part you print can vary slightly (small fractions of a mm) with different filaments, probably caused by variations in filament diameter affecting the extrusion factor, or possibly differences in material affecting its shrinkage rate. The mechanics of the printer can also affect the size (belt backlash, extruder off-vertical etc.). This can result in parts which need to have close tolerances not quite fitting. The parts supplied with the kit are good quality, but being printed they may well need a bit of sanding, drilling or filing to achieve a good fit.

When designing your own parts for printing, any dimension that needs a very close tolerance will need to be adjusted in the design in order to achieve a printed part that is exactly the correct size (which is then repeatable so long as you do not change to a different filament or print on a different machine). This is no different to traditional moulded parts, where the mould dimensions must be adjusted to account for the plastic shrinking as it cools. Due to the cost of making a mould, the amount of oversize is calculated beforehand, but with 3D prints there are also other factors at play, so the easiest is usually to get critical dimensions correct by trial-and-error. Obviously it is better to have any errors in the direction where it is possible to correct by taking a bit of plastic away, e.g. a hole that is too tight is easily fixable but a hole that is too loose is more of a problem.

Dave