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24V Mitre Saw Fixing

Long have I been jealous of Bongo’s combination mitre saw and table saw, and his ability to quickly and easily to produce accurate cuts of any angle. This was never a problem when I lived down the road but since moving away to the country I have had to rely on either jigsaw or circular saw or in the worst case make cuts completely without electrical current of any kind. Therefore I was pleased as punch when a Bosch GKG 24V (cordless) came up on a well known auction site. Sold as seen with a rumbling noise, sparks and broken bush cover. I purchased for a very agreeable price hoping that a combination of the base unit and a corded circular saw I have knocking around could produce a hybrid unit.

However on arrival the saw was in much better condition than I was expecting with all original clips, Allen keys and blade spanners attached. It spun up and cut, albeit with an angry grumbling noise and sparks but there did seem to be potential. Lets open her [sic] up and see what seems to be the problem.

To start with the grumbling issue; having removed the cover and accessed the motor (7 small screws, 2 large and 4 long ones holding the motor housing to the main gear box) the armature was exposed, held in the photo by the tight fit of the bearing. Slowly turning the saw blade by hand and watching the armature revealed a less than perfect rotation. Removing the armature completely, the front bearing was defiantly on its last legs. A quick generic internet search function later returned an exploded diagram and replacement bearings for a reasonable price on powertoolparts.co.uk.

The sparking, not surprisingly, turned out to be the bushes. These are held in by small screw-in covers but on one side had cracked and was jammed at an awkward angle, resulting in the carbon brush meeting the commutator at an awkward angle. This would have been a relatively easy super glue repair; if a little short sighted if future replacement was ever required. Fortunately the old cracked cover drilled out ok and the parts website was also able to supply a replacement cover/cap. Two minutes with a file and the bush is back in service.

 

The bearings proved to be almost as easy, succumbing to some light tapping to remove, saving the effort of cobbling together a bearing puller. Once the new ones were in place (reversed tapping against a piece wood for the lower one and using a drilled out chunk on the spindle end) it was simply a matter of reassembling the saw.

Moment of truth, attached battery, pulled trigger, click, click, nothing. Diagnosis: during the multiple dissemble reassemble operations, I had tweaked a wire on the bushes and the crimped end has gone awry, simple solder job and back in business. Pulled the trigger and it’s alive!! Grumbling muchly reduced, no sparking and faster running speed than previously.

RESULT!!! now I can cut all sorts of previously inconceivable angles, such as 30 degrees like this garden planter which was the saws first test piece.

What’s next?

The saw compliments my range of 24V cordless Bosch equipment that has blossomed since the super drill but I have an idea that a mains-to-24v power supply, that could run this saw and other items, would be a useful addition to my basement workshop. The saw also needs a better dust collection method than the current blowing it out the back method, I’ll have to get cracking on a dust sniper of my own.

 

Responses to Mobile mitre matters

  1. Bongo

    Yo Dave, nice first post! Interesting, I had never really come across a battery mitre saw before. Looks good.

    I had to chuckle at the ‘blowing it out the back’ dust extraction method – I guess this saw is designed to be easily taken outside though…

  2. Chris

    Mitre saws are great. Last year I adopted one. It was being given away by its previous family because it wouldn’t play nicely. It chewed through its safety guard and had been know to bite people.
    With some love (in the form of a new blade, removing the remains of the guard and some deep cleaning) it is happy in its new home and has helped out with almost every project involving wood.

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