Clearances on axleboxes and coupling rods

Hi There

I am designing a small (16mm scale) narrow gauge locomotive.

I want to include springing on the main axleboxes.

I am thinking that the main axleboxes, the one with the coupling and conecting rods should be a good sliding fit in the horns.

However, the other axlebox and far end of the coupling rod will probably need some play to allow for moving up and down.

Using TurboCAD the maximum length variation on vertical movement would be - .03mm

How much clearance should I allow?

Would it be best to ream both the axleboxes 1/2 thou larger than the axle

and the coupling rods the same?

Is there a formula for working this out?

regards David

By the time you have totaled up the clearances for sliding fits and the fits of the various pins and pivots I doubt its worth worrying about 0.001" of movement.

Should we also ask if you will be writing this engine up for one of the mags or one of your books in which case its for monitary gain and this post should not be here

J

Edited By JasonB on 19/02/2013 15:53:12

Hi Jason

I had not considered writing it up. If I did it would probably be for 16mm today which is unpaid.

I have nothing to do at the moment so I thought I would design and build a locomotive for something to do.

regards David

Maybe I got the wrong impression but I was only going by what you said a week or two back

"I may even design and sell a few engineering models and or tools."

J

Crikey, a magazine editor with nothing to do!!

You certainly chose the correct change of tack LOL

Is there someone else assisting with editing of MEW?

No, I do MEW on my own.

However, I tend to do it during evenings and weekends.

I am waiting for the drawings to be done.

I read Twilight last week, New Moon this week.

I will find another book for the rest of this week.

Never been so lazy.

Regards David

I meant stationary steam engine casting sets. without boilers.

Too much hassle to make complete locomotives with boilers.

Especially with liability insurance problems.

regards David

David,

Don't they go off topic quick!

The clearance rule for bearings and sliding faces is a thou per inch. In 16mm gauge that's not going to be a lot, so I would say that if you make the axleboxes just a sliding fit i.e. not needing to be forced to move but not slack and an equally easy fit on the journals you will be OK. You don't need to make any allowance for angularity in coupling rods. One thing is certain, once the loco gets running it will soon bed in and be fine.

Regards

Eddie

Thanks Eddie.

regards David

An old chum of mine used the simple rule where bearings were concerned of 'just enough clearance to keep some oil in'; always struck me as a good approach. With my average machining skills I find it easy to produce a hole that's always a thou or two too big and on my 16mm stock that works fine. Add a bit of wera in use and it runs in ok.

Robin