Cylinder Hones

[Fluffy]

G'Day All,
After honing the cast iron cylinder (Ø30mm) for my current engine with a brake cylinder hone I was not satisfied with the result. The cylinder finish up with a slightly reduced diameter at approx. the mid point of the cylinder length, just enough to stop the free movement of the piston through the bore. I used the brake cylinder hone as I did not have any other type of hone for this diameter.

Fortunately, I had ordered Issue No.16 of Model Engine Builder magazine for some other information. In the issue is an article by Dwight Giles & Mike Rehmus, on the construction of cylinder hones that use a No.2 morse taper to expand the lap sleeve. Hopefully problem solved!

I then made the components of the hone with a larger lap sleeve than the article, cutting the slots 1.5mm deeper to compensate for the larger diameter. The mandrel taper was turned by offsetting the tailstock & checking the taper with a No.2 drill taper sleeve & Prussian blue. The taper in the lap sleeve was produced by boring an undersize taper & finishing with a No. 2 reamer. All the slots in the lap sleeve have been cut with a 0.040" slitting saw. Result, fantastic.. The lap sleeve expanded easily & more importantly, parallel & solved the problem in about 20 minutes. I used 1200 grit diamond paste as the cutting medium.
If you need to make a cylinder lap I can recommend this type. Using smaller Morse tapers for smaller diameter laps should work. One lap sleeve is made from 6061 Aluminium & the other from Phosphor Bronze, both are 75mm in length. The adjusting thread in this case is Ø5/16" brass thread used for the fine pitch.
Regards,
Don.

 

[Jordan]

There's a good idea. I have MT2 reamers, so that'd be a real short cut method to make a lap.
That's just a block under the tapered arbor, to prop it up for the photo, isn't it?

Jordan

 

[MuellerNick]

Good job, Don!


Nick

 

[Till]

For understanding only: Lapping and honing are very different in result and purpose.
Lapping is a combination of plastic flow and cutting with unbound grit, the purpose of lapping is a smooth surface with improved geometry.
Honing is cutting with bound grit for only slightly improved geometry with additional grooves, eg to retain lubrication oil! (wich is not necessary in model engines due to the few power-on hours)

 

[MuellerNick]

Honing is cutting with bound grit for only slightly improved geometry

What!? Don't tell that Sunnen or Pemamo, they will get very angry.

Nick

 

[aonemarine]

I manually hone cylinders to .0002 with a rigid amaco hone and the grit of the stones determines the cross hatch. very fine grit stones and light pressure will actually polish the bore leaving very little if any hatch pattern. for small bores say 3/4" I use piston pin hones to finish the bore so that there is no measureable varience. I have never tried to lap a small cylinder so I cannot comment on that...

 

[Walsheng]

This is an interesting topic for me. I am close to the point of finishing the bore for a Stuart No. 9 cylinder (1-1/2" bore -2-1/8 long.) I was thinking of getting a brake cylinder hone but I think I will hold off and learn more.

I am planning on attending the NEMES show in a couple of weeks and was hoping to ask about this and a few other things.

John

 

[aonemarine]

the problem with brake cylinder hones is they dont hold true and can taper a bore very easily. This style of hone is more of a glaze breaker rather than a hone to finish a bore size. Thats just my humble opinion....

 

[petertha]

Nice work. Ive seen a other model builders describe similar devices. I'm going to have to cross this bridge one day soon so hopefully ok to ask some dumb questions.

I still dont quite understand the principle of how the sleeve can expand perfectly radially as its incrementally positioned up the tapered mandrel. Can someone elaborate? It would seem to me, with one (single) through-cut slot in the sleeve, it's OD would grow in an ever-so-slightly distorted fashion. Trying to wedge open a stiff, thick 'C' shape so to speak.

Maybe worded or visualized another way, take an ER collet for example. It's slots are cut from the rear & then the front alternating radially around the collet. But not all the way through the ID hole like an open slot. To my brain, the ER style would grow & shrink more even, kind of like zig-zag expansion in the radial direction, no? (Or maybe this principle is just to accomodate wider range of diameter moreso vs accuracy?).

Also, from the geometry control standpoint, is there any difference or advantage between shop made assemblies like shown vs commercial units like these Acrolaps (ie the through-hole barrel lap style)? They dont strike me as very expensive. But maybe you have to have more perfect bore to begin with beforhand?

http://www.acrolaps.com/

 

[Jasonb]

The lap only needs to expand by a very small amount, maybe 0.001 at the most so distortion is hardly noticable.

You do have to watch the brake cylinder hones as if you get too fat out the end you will bell mouth the ends which sounds like what happened to the OP.

I've made similar hones in the past with a shallow taper, they work well.

 

[Walsheng]

The 1-1/2" cylinder hone I was looking at cost about $15. I went to McMaster-Carr and piece of 1-1/2" brass is about $75 and brass tubing is about $40.
They also sell a 1-1/2" brass cylinder lap for around $30. On the plus side it is ready to use.
The brass rod is 12" long so I would wind up with a bunch left over, not a bad thing. I would need to fabricate the lap.
The brass tube is also 12" long and only 0.065 wall and I cannot see a lot of use for that left over and I would also have to fabricate the lap.

I guess I just need to justify buying the rod and the lap

John

 

[Fluffy]

Jordan,
The material that you ask about is a strip of 0.040" mild steel that acts as a key to prevent the sleeve turning on the arbor. It is a close fit in the groove in the arbor & retained with high strength loctite.
Don.

 

[Ramon]

Having lapped the odd hole or two over the years I'd like to say Don what a nice job you have made of your two examples. Being a very shallow taper though it will have to move quite a bit as lapping progresses and the lap wears. The other reservation I have of this type of lap - I have only relatively recently tried this taper method (a coarser taper mind) - is the difficulty of getting the lap to back off a little if it is overtighted for the bore. I overcame this by making the mandrel screwed both ends to enable a push from each end.

Re the honing - I can understand 'aonemarine's' reluctance in using brake type hones as he is used to a far more professional set up but I did use a brake type hone to successfully size the nine CI liners on the Bentley engine to a plug gauge - I set the hone in the drill so that it would only just expose about 5mm at each end and experienced no bell mouthing despite having to do some for considerably longer periods than others to get them all matching. That is not to imply disagreement with anyone as it is very easy to bellmouth both in honing and lapping if not taking care.

As is described on the Super Tigre thread the fine lapping of bores and pistons of small aero engines is a delicate operation to achieve an extremely good fit but can be achieved with relative ease.

Not wishing to teach granny etc but one thing to be aware of is that if using diamond paste to hone soft material eg leaded steel, cast iron etc the diamond will embed itself into the metal and will not be entirely removed by conventional cleaning (ie solvent or scrubbing). An ultrasonic cleaner is the only thing that will remove this effectively. This does not occur using silicon carbide powder which solvent will readilly remove.

Good luck with yours Don.

 

[Fluffy]

G'Day Ramon,
I did experience an over tightening drama & agree that the arbor would be improved by having a threaded section on the larger end of the taper. When I make another of these hones I will endeavour to thread part of the shank & fit an extended nut to it to enable easier removal of the sleeve. I viewed this as a learning exercise & was very pleased with the result.
Regards,
Don.

 

[BronxFigs]

I will be honing some 1.1250" inside diameter stainless steel tube. Assuming that the tube is not perfectly round, or straight, what's the best way to approach this operation without spending a fortune on commercially available hone sets, or spending hours in a shop making expandable hones?

Is there a quick way to make a serviceable hone? I don't care what the final diameter of the tube becomes, I just want a straight bore, and nice finish.

I am new at this so your help is needed. I do have a three-finger, expandable hone, but now I know that they really don't produce a straight, bore without taper.


Frank

 

[Jasonb]

Frank, take a look at Ramons copper laps on the other forum we all visit, not much material needed for them

 

[BronxFigs]

Jasonb,

I will do as you suggest. Thanks.


Frank

 

[mu38&Bg#]

Frank, I've used the Acro laps. They are cheap if you have to pay for your time. I buy them from McMaster Carr. I assume the bore will be machined to a fine finish before lapping.

 

[Bastelmike]

Hello all,

I agree with Till. Manyin this forum are confused in the difference between honing and lapping. Nearly every homemade honing tool is in fact a lap.Read Tils definitions again please.

As for brake cylinder hones, I would call them flex hones. IMO they are unfit for precision and not worth their price.

Mike

 

[Paulsv]

Not wishing to teach granny etc but one thing to be aware of is that if using diamond paste to hone soft material eg leaded steel, cast iron etc the diamond will embed itself into the metal and will not be entirely removed by conventional cleaning (ie solvent or scrubbing). An ultrasonic cleaner is the only thing that will remove this effectively. This does not occur using silicon carbide powder which solvent will readilly remove.

I'm apparently not as sharp as granny on these matters. What grit of silicon carbide powder would you guys recommend, to lap a bored 12L14 or Cast Iron cylinder? I am planning on using an o-ring rather than an iron piston ring. (This is for a Webster.) Any suggestions on where to buy small quantities?