Mini Mill Gears

Mini mill conversion to steel gears
Last updated: 05 Dec 2016

Sadly, the mini-mill digested part of its gearbox recently (ironically while cutting a gear hob). The sliding transmission gear ended up in over a dozen pieces when the spindle jammed, so a replacement for this gear is on its way along with a spare set of ALL gears in case this happens again.

	06-Dec-2002: The replacement gears have started turning up. The white gear on the right is the existing static transmission gear which did not disintegrate, although it's a little rough round the edges. Shown on the left are the new motor pinion and gear - the pinion is metal.
	Exercise care when knocking the spindle through the bearings. The material is a lot softer than I was expecting and the end of the threads got mashed with almost zero effort. On my mill, the spindle is a slight interference fit in the bearing bore so if you need to take it out, make up a mandrel and hydraulically press the spindle out to avoid the kind of clueless mistake I made here.
	Luckily the spindle thread cleaned up OK on the Myford using the nifty ML7 gear calculator to work out the change wheels for the M27 x 1.50mm thread. Phew...
	The gearbox divested of all its innards. For reference, the bearings are metric and are plain ball bearings - not taper roller or angular contact. The large bearing is 62mm OD x 30mm ID x 16mm type 80206 which cross refs to SKF type 6206ZZ. The small bearings for the countershaft are type 80101 which appears to be SKF type 6001-2RS (28mm OD x 12mm ID x 8mm).
	26-Dec-2002: Still no gears, still no milling machine. The kind folks at GLR have cut me up some steel gear blanks, so I've started making a metric module 1.5 hob from some 3/4" Silver Steel (drill rod) to put some teeth on them. The gear hob has its own project page you can get to by clicking here.
	28-Dec-2002: Thanks to the nice people at LittleMachineShop.com, the new gears have turned up. Just as soon as the rotary table stand and tailstock are ready, I will be able to cut some gears...
	7-Mar-2003: Rotary table bracket/tailstock are complete, as is the hob - these items have worked out well so far. Should be able to make the 30 tooth motor gear before too long.
	16-Mar-2003: This is the 30 tooth gear that meshes with the motor pinion. Something is not right, the teeth look the wrong shape and the hob used to cut it is bent (during the heat treatment?). It has been fitted to the mill, but it's noisy. 28-Mar-2003: Doh! No wonder it's noisy, pressure angle is the angle across both faces so I've ended up with a 40 degree pressure angle hob and gear. More work to be done...

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