Bolt Patterns and Clearance

bolt-clearance-02Sometimes I just struggle to get the correct clearances and bolt patterns. Often due to the fact that I change my mind on the type or size of bolts that I should use.

The trouble is the model is in my head and in that space it works, whereas in reality I haven’t left enough space for the heads and so they hang over the edge or they don’t clear another surface.

The result is I end up machining both the part and the bolts, removing material from both to scavenge some space.

Normally there is just enough material to create a clearance, such as the end result for the bolts that fix the cylinder to the main body of the engine on the right. I did have to machine the high tensile bolt heads of the capheads which wasn’t easy, even using tungsten carbide tipped tools these bolts are rather hard.

Unimat 3 Pillar Drill
Unimat 3 Pillar Drill

I marked circular distance in from the edge of the cylinder on the face that is not seen. I then mounted thisĀ in a small unimat 3 jaw chuck and mounted this onto my small pillar drill in place of the table – the table unscrews from the 14x1mm mount.

unimat3drill-015The dividing head, shown on the right before the main body was powder-coated. This allows me to then use a small centre drill to mark the position of the 6 holes very accurately. This simple dividing head allows me to mark 2, 3, 4, 5, 6, 8, 10 using the basic 6, 8, 10 holes that have been accurately placed in the mandrel using a clock dividing plate as a reference.


About Nigel 203 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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