Cylinder bore surface?

Hi folks,

I am in the process of building my first engine ( the Julian De Waal beam engine) and am about to start the cylinder and valve chamber. I am wondering how to finish the bores of the cylinder and valve chambers. I suspect that internal boring will not leave the surface smooth enough. Will I need to buy a “Cylinder Hone” to get a decent finish, and if so how much metal do I leave for the Hone to remove? Any info. would be appreciated.

Thanks, Malc.

Malc

I think that, for a steam engine, a finely bored finish should be quite OK

Norman

Honing primarily removes the tops of the ridges from previous machining marks. Whilst it is possible to remove some measurable amount of metal I think this unlikely from a model engineers point of view. Think of it as a surface finish conditioning process, use were a non metallic sliding seal is used at high pressure.

.

Depends on how good the bored finish is if you need to hone or not. - But in short a honed finish will always be better. If the boring has done a reasonable job leaving 1/2 - 1 thou I would say would be enough.

It would also depend on if you were using a cast iron or an O ring. A rougher surface would chew up the rubber / viton ring, while a cast iron ring would eventually hone the bore this might take a long time and still run the risk of the bore and ring ending up scratched.

Most people want a nice slow running engine on a wiff of air for demonstration purposes and not one running uber fast. Again a nice smooth bore will assist in this.

So in short I would hone which is going to give a better finish than even the best bored out cylinder. Especially if the cast iron is not 100% good as some is nicer to machine than others.

Nick

Edited By Nick_G on 27/02/2017 18:28:04

I like to give my cylinders a quick lick with a brake cylinder hone particularly if using O rings or in the case of Jan's beam teflon rings. Not quite as critical with iron rings

Amount to allow will really depend on how high the "crests" are from your machining but something liek 0.001" -0.002" would be about right. Its not dead critical as you will make the piston and teflon ring to suit the bore.

The piston valve hole is too small to fit a hone into so ream that which should give a good enough finish, you can always lap the valve spool into place with some lapping powder or even metal polish.

Hi folks,

Many thanks for the advice.

Malc.

I used to burnish small cylinder bores on hydraulic cylinders. Basicly a tool similar to an internal knurling tool but with a roller bearing running on the cylinder wall.

"Ballizing" is pressing a hardened steel or carbide ball through the bore to improve the finish.

Hillbiilly hone will do the job. Bit of dowel with a hacksaw slot in the end and a strip of emery paper or wet rub inserted. Wind the paper around the dowel a bit, insert in hole and spin with pistol drill. Works on holes smaller than a brake hone will get into too.

How about using flex hones, especially for holes smaller than the normal hones do.

They go down to 4mm.

You have to be very careful with flexi hones, as they follow and exaggerate any ovality. We banned them from our Hydraulic workshop. They are fine for a quick polish up but don't try to remove any material with them.

With my Stirling Engines I use a wooden lap, i usually finish with a fine grade of grinding paste, but I have used metal polish/Brasso, Silvo, or toothpaste, free airline toothpaste is quite fast cutting. The Stirling Engines need a polished bore, unlike a steam or IC engine with cast iron rings.

Ian S C

The other thing with Flexhones, is to CLEAN everything afterwards, I think that they advocate scrubbing with a nail brush.

You cannot afford to have particles of Silicon Carbide around. That makes running out compound, not running in!

Howard