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Cordless Blue Biax retro-fit


Mar 28, 2007
England UK
I had a pile of bits left over after a repair session so I decided to see if I could retro-fit a cordless motor onto an incomplete and otherwise useless blue biax.

Here in the UK we have a store called Aldi which are known for supplying very cheap hobby-grade power tools. I bought one of their £15 cordless grinders because it looked like it would be a decent match. (Of course I needed a battery and charger which are sold separately so I bought a grinder/battyer/charger combo and a second grinder to modify).


First strip the front of the grinder and pull the motor housing off complete. Luckily, the front bearing is the same size and the spindle end very similar. I needed a 9mm thick spacer plate that I could screw to the motor and then screw the gearbox to the plate. If you're going to make one of these you need a 51mm through-hole to locate on the Biax gearbox (then afterwards you have to die-grind/mill out some exhaust vents).

spacer plate 1.jpg
spacer plate 2.jpg
Now the grinder has a bevel gear keyed to a plain 8mm shaft but of course the Biax has a 0.7module 6 tooth spiral gear on the armature. If I had a scrap armature to butcher I would have transplanted the end onto the grinder armature but I didn't and I couldn't make a spiral gear so I made a straight 6 tooth gear instead.

pinion 1.jpg

I clocked the armature in the 4-jaw and turned the end off it then bored it our to accept the new pinion

pinion 2.jpg
Pinion fixed in place in the armature.

pinion 3.jpg

Now I assembled the whole motor onto the gearbox plate and cut a matching gear for the pinion from delrin. I had to borrow the layshaft from another machine as that is one of the bits that I am missing.

Pinion gear.jpg

After that it was just a matter of assembling the machine.

Cordless biax.jpg

And yep it works great. Has plenty of power from the grinder motor. Runs nice and smooth just probably 10% slower than a mains motor one (no bad thing), no more or less noisy than the original. I ran 3 heavy passes over a 10x8 scrap surface plate and it only went down one light on the budget 40V battery. It's fixed speed only but I am looking to find a way of speed controlling it. There are several options on Amazon/Aliexpress but so far none that will fit inside the case. Project for another day.

Cordless Biax tested.jpg
By the way folks I need this part. The one I have is borrowed. I don't need the plastic/fiber gear just the metal shaft.

Fiber gear carrier.jpg

If anyone can help me out with this it will save me a lot of trouble. I could also do with a replacement front housing, in aluminium if there is one going spare. I don't need any of the moving parts.

Also, I could do with a blade carrier. Mine is busted.

blade carrier.jpg

Small update to this I swapped to a different motor which is brushless and has speed control built it. Still very cheap at only £35 without the battery.

18v Biax.jpg

It's a much neater install which involves modifying the ally end plate of the grinder and the end cap of the Biax gearbox so that they will mate together but the result is far better than the original.

biax mod plates.jpg

It will use Makita batteries whic are plentiful:
Here is how I fitted the pinion. I had to make a straight tooth pinion since I didn't have a biax donor rotor but if you had a dead armature you could chop the end off it.

I cut the rotor back to the bearing diameter then bored it 4.3mm to tap for M5. After that I counter-bored it 6mm. I made a new end with a 6 tooth 6mm dia gear, 6mm OD and a loose fitting M5 thread. The pinion simply screws into the rotor.

armature pinion.jpg
Peter has taken 2 or was it 3 of my classes. One in Norway and done in the UK where he is from. He helped organize the UK class. He is a really cleaver man and a hell of a good scraper. For his first class he adapted a variable speed switch he installed in a blue BIAX. It may have been this blue scraper? Cleaver as hell. Peter used to dig huge tunnels under London for his real job. You still do that? If my memory serves me right, Peter is the good looking guy in the red and white striped shirt.