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New Bush - steel, brass or...?

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Andy Carruthers20/02/2019 13:30:00
227 forum posts
23 photos

My donkey saw (acquired, home-made) quit today

Drive goes from electric motor via belt to large pulley which has a small sprocket on the back connecting to a large geared wheel which drives the arm back and forth

The large belt driven pulley has a bush between itself and the spindle, and it is the spindle (think old steel bolt) which siezed, on dismantling the spindle is gouged whereas the bush looks ok - not that I can re-use it

I plan to turn the spindle down and make a new bush, the question is, what material would be best to use?

Emgee20/02/2019 13:37:15
1088 forum posts
199 photos

EN8 may be OK for the spindle, is there enough metal around the area to use a sealed ball bearing ?


Andy Carruthers20/02/2019 13:48:58
227 forum posts
23 photos

Bush is 20mm OD 16mm ID and 67mm long, spindle was a close fit, it's all a bit Heath-Robinson which is about my ability level

I have some 15mm OD 6mm ID sealed bearings, I think the spindle will be too small diameter given the length


Martin Kyte20/02/2019 13:59:40
1419 forum posts
9 photos

Well if it's Heath Robinson, Lignum Vitae would be more in keeping. Seriously what usually happens is hard particles embed in the softer material which then wears the harder surface. Old clocks do it. Dust particles embed in the brass clock wheels and erode the hardened steel pinions. How long did it take to wear out with the original configuration. If it's 10 years or so you may as well just do the same as last time.

regards Martin

Andy Carruthers20/02/2019 14:49:51
227 forum posts
23 photos

I acquired the beast a couple of years ago, age very hard to tell

I take your point regarding the bush, it is stainless steel and (relatively) unmarked, regardless of which, it's unusable anyway

I may drill an oil way half way down and replace the bush with a mild steel one which apart from brass is all I have and see how it goes - at least I have the benefit of more knowledge than when I started

Martin Kyte20/02/2019 14:55:18
1419 forum posts
9 photos

Generally best to use dissimilar metals. I'd go for brass. Lubrication would be a step forwards though.


Andy Carruthers20/02/2019 14:58:14
227 forum posts
23 photos

Thanks - I'll go with brass

not done it yet20/02/2019 17:12:32
2899 forum posts
11 photos

Consider a couple of needle roller bearings and a spacer?

If going the bush route, a lubrication groove (such that any foreign bodies are gently displaced towards the ends) would be a good addition

Hopper21/02/2019 04:15:33
3593 forum posts
72 photos

Sounds like an ideal application for a sintered bronze bushing aka Oilite. But if you have brass in the workshop already, that would be a better choice than steel running on a steel spindle.

Andy Carruthers21/02/2019 07:15:45
227 forum posts
23 photos

I turned the spindle down to 15mm, drilled an oilway and made a brass bush, I will look at creating a lubrication groove later, then reassemble

Thanks to all for your advice - appreciated

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