Toolpost Grinding

[Joe PageParticipant @joepage27051]

Hi everyone, new to the forum.

I'm making an IC engine and want to use mild steel, I'm not trying to make it last, I'm just wanting to experiment with different designs and do it cheap as possible.

I'm sure everyone feels the same with mild steel regarding the finish, the only real way to get a good finish is to sand it afterwards. I'm wanting to make the cylinder liners out of it, 30mm bore, around 45mm cylinder length.

So I have been looking into some way of grinding in the lathe. I made a toolpost holder for the bench grinder, but I only have a crappy wheel that came with the grinder, a diamond wheel which I later found is no good for anything but carbide and a cbn wheel which is no good for soft steel.

I want to spend as little as possible, but I have a couple of questions;

I have some die grinding wheels to do the bores, is 3000rpm fast enough as I can modify the grinder to hold collets, if so, should I get something like a white wheel for the grinder to do the outside of things.

There is a bosch die grinder that I can buy which can be mounted. Not sure how long the wheels last, but would I be able to achieve a bearing surface, and would I be able to achieve a parallel bore – how fast do they wear. They are the cheap dark blue kind, should I look for something else.

Or any other recommendations

Help would be greatly appreciated,

Thanks, Joe

[Joe PageParticipant @joepage27051]

[JasonBModerator @jasonb]

Depending on whether you are using piston rings or not the usual ways are to either hone or lap the bore. A hone is best if using cast iron rings, a lap if using O rings or direct metal to metal piston/liner.

Lapped steel bore

Poor picture of a honed iron bore

Good thread on lapping and honing for models here

Edited By JasonB on 20/09/2015 17:54:27

[Joe PageParticipant @joepage27051]

Hi Jason, thanks for the quick reply.

I remember going down the wood and sandpaper mandrel route a while back and it took ages to get by desired finish. I suppose it's me trying to find a shortcut, thinking about it I never had carbide inserts back then, so I was probably trying to lap out reaming marks.

I do however like the laps on the link you gave me, so I will have to give it a try. I think grinding dust running through my lathes coolant system is probably a bad idea.

[Paul LousickParticipant @paullousick59116]

Hi Joe,

Use a car brake cylinder hone. They are a smaller version of the spring loaded hones that are used to finish a car engine cylinder and not expensive  Available from car accessory stores and *-bay.

Paul.

Edited By Paul Lousick on 20/09/2015 23:55:04

[Ian S CParticipant @iansc]

To quote from James G. Rizo in his book "Modelling Stirling and Hot Air Engines", Using a wooden lap"The longerthe job takes the better the finish to the bore". It's the method that I use, some times with the use of a brake cylinder hone first.

Ian S C

[Paul LousickParticipant @paullousick59116]

The cylinder surface finish does not have to be mirror smooth but should and have a crosshatch pattern so the cylinder walls will retain oil and provide adequate lubrication for the rings.

Also important is bore geometry. The hole should be as round as possible with little or no taper or variation vertically. Bore distortion caused by deflections in the casting or improper boring or honing techniques will have an adverse effect on ring sealing and blow-by.

Paul.

[john carruthersParticipant @johncarruthers46255]

I'm looking at using a flexy drive to a chuck held in the tool post. I currently use a mini drill bolted to the cross slide for light grinding.

[Joe PageParticipant @joepage27051]

Hi guys, thanks for all of the replies,

I think I will go for a hone to see how that turns out, I turned some mild steel yesterday and the finish came out pretty good so hopefully it shouldn't take a great deal of lapping.

Now there's two hones to go for, the shoe type or the flexi-hone type. In all of your experiences what do you all prefer, and if it is the shoe hone type then are the £7 ones on ebay any good or should I go for something with a better quality,

Thanks,

Joe

[Roderick JenkinsParticipant @roderickjenkins93242]

Joe,

This recent thread **LINK** discussed various hones.

Rod

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