Reaming 12l14 steel

[kylenlord]

Hi everyone,

I’m looking for some advice on reaming 12l14 steel cylinders for an I/C radial.

I tried my luck at boring on the lathe but struggled with consistent results. Either my surface finish was nice but size was off, or I’d try to remove too little and have a rough finish. My sweet spot was .030” per pass.

I’d like to use a chucking reamer setup in the Bridgeport. Set one cylinder up at a time, follow through drilling and reaming and then reset another cylinder blank.

Is this a silly idea, or is this feasible? McMaster has reamers in .998”, .999”, .9995” and 1”. Will the finish require lapping, and should I go undersize? The final bore size is 1”.

I also looked into cheaper reamers in 1”. Is that a waste of time and money to try to save $70 on this tool?

Thank you for any help,
Kyle

 

[Cogsy]

I've reamed bores in 12L14 and it works perfectly. I would never lap an IC piston (provided you're using rings) as you want the rings to seal, not the piston. A lapped piston with rings is just creating more drag for no benefit.

Being that you're making the pistons (I assume) then the final dimension of the bore isn't really critical, as long as you know what it is and make the pistons to suit. So long as the cheap reamer provides an acceptable finish then it should be fine, and you just make the pistons to suit. If you use the same drill bit and reamer for each then they should be the same.

 

[Rustkolector]

Kyle,
I have never experienced difficulty reaming 12L14. You should only remove .008"-.015" with a chucking reamer. No more. There is very little chip space in reamers so light cuts work best. I prefer to drill, bore, and then ream for straightest bores. However, in my opinion reamers rarely give you an absolutely round bore good enough for piston rings without some honing or lapping. Other options for cylinder bores are DOM (drawn over mandrel) steel tubing or hydraulic cylinder stock. You can get the bore size you want but will have to trim the OD. DOM should have a little final honing, but doesn't usually need much.

12L14 is a great metal for a lot of things, but not my favorite for cylinders. Some like it for cylinders, but this metal rusts so easily that you have to use heavy oils or squirt your engine bores with WD-40 especially after short runs. The remaining moisture from combustion gases in a cool running engine can be significant. After short runs immediately spin the engine over a dozen revolutions with the ignition off and the throttle wide open. This should clear the cylinders of most of the combustion moisture, but not all so don't forget to use WD-40 or other light lube before putting your engine away.
Jeff

 

[tornitore45]

In order of precision, roundness and location:
Drill: Awful
Double drill: Bad- depends on what is expected
Reaming after drilling: Will not move a hole location, will make hole a bit more round with a better finish
Boring: if done correctly guarantee the best roundness finish and even move a hole into location.
Reaming after boring: A waste of time and possibly degrading the hole roundness.

 

[kylenlord]

Thank you guys for the feedback. I didn't occur to me to bore on the mill with a boring head. I'm in the process of acquiring one. I think I may give that a go first, to see what I can come up with. If that doesn't pan out I suppose I can try to reamer after getting the bore close to final size.

I'd never used leaded steel before this, it was just the recommendation from the plans.

What cutter is preferred for the boring head on 12L14? I have a few brazed carbide styles or I can setup a HSS bit.

Thanks again
Kyle

 

[tornitore45]

For the best finish HSS with rounded tip and some rake.
Carbide is OK but may not cut the last 0.0005" reliably.
If the part allows it, I rather bore on the late that on the mill. I found easier to control the diameter and if the part is balanced it can spin faster that an inherently unbalanced boring head.

 

[jquevedo]

I used leaded steel to make 1 inch diameter liners for a flat four aero engine, with great results.
My process, lathe drilling with drill to close size, then boring in lathe with Carbide boring bar ( biggest diameter you can use will provide less chatter and better finish.
And then finish with a HONE not a reamer, I set one liner to the size I ,m looking for and then finish the rest at the same setting. I place the reamer in the lathe chuck and use a holding fixture to hold the liners while I HONE them.

 

[kylenlord]

Hi Jquevedo,

Could you please elaborate on the hone that you use? Is it the finger style or the ball type? I did another test using the indexable carbide boring bar to get me close to final dimension and then finished with a brazed carbide taking about 2-4 thousands per pass, and I was able to sneak up on .998" comfortably. I'm feeling a bit more optimistic about this approach.

Thanks again,
Kyle

 

[jquevedo]

Kyle:
I use one of those Brass expandable hones, I think they call them Barrel laps, i bought a couple of them many years ago, mostly use the 1 inch one.
Use some clover grinding compound and clean the cylinder very nice with gasoline / kerosene.

Some people prefer to use Time saver non embeding compound.

One trick I learned from an experienced machinist was to ONLY take the cut with the boring bar in the Right to Left direction ( assuming your piece is secured in the chuck) and then back out the tool before moving it left to right, then returning to the previous setting and then cut again, this prevents the hole from becoming conical due to change of pressure in the boring bar when shifting direction.

I have tried it and it really makes a difference.

Here is the link to one supplier of laps / hones in USA, you can buy replacement barrels..

https://www.mscdirect.com/product/details/05060074

 

[tornitore45]

A boring bar has the same deflection at the mouth of the bore as it experience at the depth of the bore. The flexing is determined by the stick out length from the tool holder, a dimension that does not change as one moves deeper into the bore. The lead angle has some effect but only at heavy cuts. If the front edge slants back then the flex is reduced by the resulting radial component of the cutting force directed away from the bore center.
Obviously things reverse if the front slants forward but I never seen such and see no reason for.

It is custom to make several "spring passes" in and out without moving the cross slide when you are near the final dimension.
Once one moves the cross slide any attempt to make a final adjusting cut is in danger of overshooting the target.

 

[jquevedo]

Kyle:

While I agree with the spring deflection from the boring bar based on overhang and rigidity of tool i.e carbide vs HSS or steel with brazed tips, the angle of incidence of the tool in the wall of the inside will change with the change of direction caused by the lathe tolerance in the guides guides and cross slide.

I also agree with the final passes done with no more cutting advance instead just letting the tool taking the final cuts to recover from the spring deflection.

As always, things are not cut and dry when it comes to skills, equipment, material and all other varibales.
I advise you experiment and find the best approach that fits you and your equipment, I have been building model engines for over 15 years, you call it, V8's, radial 9, radial 5's (three of them) and several 4 cylinders as well as twins and so many singles I can't recall them all, and I have used the technique I described and have had better results than by going in and out of the bore in the same setting, so USE the process that fits your skills and equipment and allows you to achieve the desired results.

Kind regards

Jaime

 

[kylenlord]

Thanks for the help everyone. I figured I’d have a bit of a learning curve on this.

I got in a barrel lap, a perk of having a McMaster account at work, I also got the value tin of 120 and 240 Clover lapping compound. I’m not sure if I’m in the ballpark here. I tested the 120 which seemed too coarse so I stuck with the 240. I can still see some faint machining marks but I can’t feel any irregularities. They feel smooth, though slightly more rough than my best finish passes I had gotten with turning the outsides down.

Thanks again for the help
Kyle

 

[tornitore45]

I see circular rings. Are you moving the lap axially at a brisk pace.
Move fast and revolve slow to obtain a cross hatch pattern.
The finish look still a little coarse for a piston with cast Iron rings where you want a fine cross hatch pattern to retain oil.
For Vitone O ring or a lapped steel piston you want a mirror finish.

The last picture looks good, unless is the same as other with a different light.

 

[Wizard69]

This thread brought up a question, if leader steel rusts too fast what is the ideal alloy for a cylinder? Is there a “perfect” steel for use here or should we focus on cast iron?



As for some of the original posters questions:

1. Are cheap readers worth it? That is a $1000 question certain to lead to a lot of opinions. Ultimately it comes down to finding a trusted supplier. You can’t just randomly do business with a supplier in China and expect to get good results. So people with experience here are your best guides to quality suppliers.

2. After seeing the cylinder in the pictures above I’m not sure why you would do this on a mill. If you surface finish isn’t good, look into your lathe technique and the grind o your cutter. Leaded steel should bore well on a lathe.

3. Reamers don’t solve every issue one might see In machining but in this case I don’t even think they are needed. Cylinders are usually finished by honing to a suitable finish after boring. At least that is how it was done on the few big engine rebuilds I’ve been involved in.

4. Oh by the way, even though it was mentioned above, I can’t stress hoW important the old in and out is with honing. You do not want your hone (of any type) sitting in the same spot while rotating. Even if you are trying to work a specific area in the bore the hone still needs to be stroked in the bore. Shorter strokes when working specific areas longer when doing the whole bore.

5 in an IC engine the absolute size of the bore isn’t as important as the surface finish of the bore. With in reason anyways. A poorly finished bore that is on size will likely have issues. In model engineering you generally have the ability to fit parts so hitting dimensions isn’t as important as say in a race car rebuild where the pistons come pre-machined. This is why bores are often done first and pistons adjusted to fit in the model world.


As an aside I once spent a year working with a machine tool rebuilder that was extremely talented. The tolerances on IC are actually fairly large. I once spent a few days with him hand fitting a piston for a hydraulic cylinder on a big grinder. By the time he was done I would have to say the fit was within a couple of tenths. By the way no piston rings just a very tight fit for the entire stroke of the piston. As a 19 year old at the time I was most impressed. The point here is that with enough time you can achieve almost anything. With an IC engine you really don’t need to overthink the fit, it just has to be right for the design.

 

[kylenlord]

Hi guys, thanks again for the help. I think my lapping technique was way off, rpms too high and not moving forward and back fast enough.

The reamer idea was mostly just an idea in terms of speeding up the process. It takes me some time to bore on the lathe, just trying to think of a way to expedite the process. I bought a boring head from my neighbor, though I have yet to use it and those cylinders were bored on the lathe.

I think that I am trying to hard at this point to nail a the perfect size, rather I think so careful scrutiny is in order trying to nail the finish I'm going for, then figuring what was removed to get there. That way going forward I can figure how much material I need to leave.

I'll keep at it, until I come up with an acceptable finish and post the results.

Thanks,
Kyle

 

[tornitore45]

You are still overthinking.
The objective is get a bore round, ever so slightly tapered with a good finish and within 0.010" of size.

A boring operation on the lathe can get you almost all the attributes but the finish an the slight taper must be achieve with a hone.

The hone will not compromise the roundness achieved by boring but a reamer may. Reamers are better than drill bits but not as good as boring.

The hone will remove on the order of 0.001" or less on the diameter so going off size is not an issue.

A hone removes so little material and so slow is hard to throw a good part off size.

Why round?
Because is hard enough to make ring round to match a round bore, is impossible to make a ring to match an elliptical or not round bore.

Why Taper?
The slight taper is to have good compression when it count, in the top half of the stroke, and lower friction where compression is not so important.
Guaranteeing that kind of taper by boring is not practical so the hone is worked until it feel progressively tight in the cylinder top and loose at the bottom.

 

[Cogsy]

For the vast majority of engines I disagree with the taper, even a very slight one, although it's not likely to cause an issue in little-used models. In full size or high use engines, tapered bores for ringed engines are not best practice, due to the induced wear of the ring grooves from the constant expansion and contraction of the rings (and I guess even the energy losses from continually compressing the rings every stroke). I understand the max taper for full size applications is of the order of 0.0005" and this is over a bore that may be 4" long or more.

In model engines it may not be much of an issue but the potential gains in friction reduction would be minuscule and the potential for inducing piston slap and creating more friction would be high. I'd go for a straight bore every time, although I know the tiny ringless diesel engines and ringless ABC sytles do need need the taper.

 

[Mark Duquette]

12l14 is a free machining steel. Where I worked we used cemented carbide or insert tools to machine this material. It should be possible to take final cuts of as little as .0005" using a sharp tool with a small radius.

 

[tornitore45]

final cuts of as little as .0005" using a sharp tool with a small radius.

Where you work they probably have husky rigid machines and an assortment of carbide inserts perfectly matched to the task.

 

[kylenlord]

Hey everyone,

After more testing I have more positive news I believe. This is the results with a carbide tipped boring bar running 2050 rpm with .003” feed rate with between .001” and .003 depth of cut.

The 12l14 is a very interesting material to work with. Even when I’m drilling I can go right from a 3/8” to a 15/16” drill.


I also did more testing with the barrel lap, slower speed and faster left to right is much more convincing. I’m gonna get all the pieces I have made so far up to the same dimension, then finish lapping after I turn the fins and other bits.

Thanks again for all the help,
Kyle