Reed 3P armboard mounting

Mount the armband, measure accurately from the spindle and mark out hole centres.

Rule of thumb is measure twice, cut once.

Cut holes 1mm oversize, this will give you enough wriggle room to ensure accuracy.

Use nuts/washers on the underside of the armboard - this will be far more rigid than using inserts.

Personally I would not use wood, it is not rigid enough. Try aluminium or gunmetal.

There are plenty of small engineering shops with small scale manufacturing CNC machines. If you can provide an a drawing with accurate measurements, the cost of cutting an armboard is not huge.

My Reed 3p screwed directly to the teak wood armboard and fixed with nuts. I have a template with my tonearm from the manufacturer.

I think you don’t need threaded inserts if you can’t make precise PS measurement.

If you have a protractor like Feickert NG you can check PS quickly and easily.

P.S. Manufacturer recommended WOOD (not metal) armboard when I asked him about it long time ago.

I do. I have two Reed 3P's. See my profile. My advice is to not sweat it. You do not need inserts, assuming an armboard of say 3/8's or greater of hardwood. As I have stated multiple times in this forum and only had agreement from the experts here, P-S is not an exacting spec, assuming a slotted headshell. Your cartridge and stylus have no idea about and don't give a crap about P-S so long as the stylus hits the desired null points. Proof lies in the modern SME methodology. With modern SME arms there are no headshell slots-the cartridge can only be mounted in one fixed position and the solution is to slide the tonearm mount closer or further back-CHANGING the P-S! There is an invaluable lesson to be learned by the SME method of obtaining alignment. The take-away is that as long as the cartridge can be fixed in the headshell to meet your two preferred null points you are perfect. 
The exception COULD be if you rely on an alignment tool similar to a Mint Protractor that is custom made to a given P-S. In that situation, without exact P-S, your custom made protractor is of little use. You can still get perfect alignment using a universal tool like Feickert's though. So let me say it again-with a Reed 3P you can be 2-3 mms off either too close or too far and be fine with most cartridges. Beware too of cartridges that have abnormally long or short cantilevers. 

Think of it this way btw-the specified P-S is meant to permit the user to align the widest variation of cartridges in terms of mounting screws to stylus distance. 

Proof lies in the modern SME methodology. With modern SME arms there are no headshell slots-the cartridge can only be mounted in one fixed position and the solution is to slide the tonearm mount closer or further back-CHANGING the P-S! There is an invaluable lesson to be learned by the SME method of obtaining alignment.

Nothing new here, Luxman made it for ALL tonearms on PD-444 in the 70’s with metal armboards on the rail (can be moved to the left or to the right to change PS distance).

Nowadays Feickert did almost the same on his turntable.

*New SME tonearms are the ugliest on the planet in my opinion.