To ream- to lap-to hone?

[Naiveambition]

building my first I.c. engine and have been reading up on how to properly finish the bore. The bore will be cast iron and is undersized .003 with finished bore of 1.5 inches. The plans call for lapping to size and my bore is pretty rough from cutter issues. I am not worried about a little oversize if needed Just kinda lost on which process I need.

 

[goldstar31]

In your previous post, you informed us that you had a 'an inline boring bar- of sorts' and as such, the consensus of opinion was that despite its bebt configuration, it would work.

All that really remains is the continual questioning from all and sundry of how to actually grind and then hone the cutting tool-- before all this additional questioning about how to get a workable bore from
1, reaming.
Do you really expect that sticking a 1.5" straight reamer is going to fit on a little frail 7x10 lathe? Or worse, that you are going to poke an adjustable reamer into the hole?
2. honing
Ask yourself the question of how much metal can be removed with a charged lap? If you have something like Buma boring bar and start with abrasives the size of paving stones and progressively get smaller and smaller grits. I've been present when my full size 997cc Mini Cooper block was overbored +20 thous. My tame boring expert was wearing his brown trousers in case we hit 'porosity'. All that he was doing was re-boring an 848cc A series block back to the same bore as a standard Mini bore-- but I was the 'new boy' and he was 'ever so experienced'. Hummmmm!

So 3 is to what no body seems to appreciate is that boring is actually 'internal screwcutting' and if you can get a fine finish on the outside of a part with a lathe tool, you should have no difficulty working on the inside of the same block of metal.

The-- and only then, does one remove the tiny crests of what is essentially a screwcutting operation.

And NO, the foregoing isn't in any book that that I've read. What is in the books is it is the tiny bit at the end of a boring bar( or lathe tool) that makes the difference.

You asked the question, I hope that you will not be too upset with my answer.

Regards

Norm

 

[Jasonb]

What type of ring if any are you using on the piston as that affects the finish you need

 

[goldstar31]

I was curious to know whether our OP had read 'Ron Moulton' mentioned today.

I got quite nostalgic about making jet engines again- but perhaps my insurance policy precludes such Dante's Inferno activities now
.N

 

[Naiveambition]

Rings will be cast iron also. Goldstar, I'm not sure exactly what you are trying to say but comment is appreciated. I'm in new lands I've never attempted before and have no one to question my builds about. Which is why I post a lot of single questions. I do an immense amount of reading but am usually filled with many options at the end . Most times I will take a consensus view and go with it. This model is getting $$$ already so if I mess up 200$ down the drain.
As for reaming, yes you are right it is not expected to work on a 7x10, I also have a Southbend 9 used for this model. I've had so much trouble with cutting finish on this lathe. Which I'm finding out that my drive gear is to small to produce a fine finish. I've tried many diff. Cutters from hss to carbide. My roughing came out better than my finish cut.
The line boring was considered to straighten the bore after press fitting, but with my cutting problems I chose to build a large boring bar , which worked and cut good but not a great finish. I've read that most cast iron needs a slow rpm and feed, but my finishes are opposite, meaning the more speed I use the better my finish gets, why? don't know no one to ask

 

[goldstar31]

Trying to imagine what is actually going on- and causing a rough finish- and contrasting it with 'having read a lot', I wonder if you have reached the point of reading what- say- George Thomas had to recommend in both his boring tools from the tool post and again, from his inline boring bar.

Thomas goes on to describe using a final abrasive grit of a softish 100 grit but obviously honing was far finer than that. Again, he illustrates a simple tool and cutter grinder which became the now unobtainable Kennet and now the Worden from Hemmingway kits. OK, I don't like[ actually I binned a Worden, but using a final honing of perhaps an Arkansas stone will astound you.

I=f you haven't reached this concept for hss bits, you sre missing something. This, of course, reflects in why you raised your initial concern.

I create rough and ready tools with an 80 grit wheel and a mere touch with a 600 grit diamond stone. When I want something better, I head along the Arkansas trail.

Does this help?
\
Norman

 

[WOB]

If you can finish bore straight and true to about 0.002" undersized with a reasonable finish, then all you need is a 1.5" Flex-Hone as shown here:
http://www.brushresearch.com/engine-hone.php 240 grit would probably work well. It will leave the proper cross-hatch finish and will not change the shape of bore. Cast iron rings should seat quickly if they are made properly.

WOB

 

[Jasonb]

I've done quite a few open crank hit and miss engines around the same 1 1/2" as yours and have always honed the bore with one of the cheap 3 stone "brake cylinder" hones and they all run well. Hard to say if they will work on your bore as what one person may call rough would be acceptable to another.

When it comes to boring make sure you have a stout bar, the short one is 28mm dia and the longer 35mm. if it is too thin the cutter will get pushed off the surface and you may get chatter.

 

[Naiveambition]

Thank you thank you thank you... Just what I needed. I had looked at the flex hone and in research had showed "if" the bore was not perfect straight it would not correct. So onto lapping, it seems to straighten the bore but also leaves a really smooth finish. I'm pretty sure I have a straight bore from measurement but does have a .001 oversize at the far end. If the flexhone or stone hone will work then that's what I will try.
As for the cutter bits yes you are correct I am missing something. Outside turning I can do sometimes with hss but not boring. I have better luck with harbor freight carbide cutters. I can get better finish on my 7x10 than the SB 9. I do tend to use more speed and seems to help. Most literature shows very heavy cuts on the SB 9, more so than what I feel comfortable taking.
With this one I noticed that no matter what cutter I used , the finish was the same under powerfeed, od or id. I do need the 80 tooth feed gear, then I think a lot of my issues will go away. Still need more training on hss geometry so will listen intently to all of your suggestions, as I will need to line bore the bearing caps

 

[goldstar31]

For a bit of internet reading, I would commend Conradhoffman.com, Advance Tool information.

It deals with 'grumpy old men's attitudes too but it does concentrate on how cut metal with hand produced tools or simple tools. It's an idea to make up a simple jig not unlike a hockey puck and rub your tool on a very fine membrane of diamond particles.

As I have said that I don't work with one because I have enough more orthodox tooling which at a push will make the 1/10th diameter milling cutters to do a vee 12 engine from scratch. Prof Chaddock did!

Try the Hoffman thing and I have no doubt that you will be amazed at how efficient it is

Regards

Norm

 

[Naiveambition]

Re

 

[XD351]

I machined the liner for my hit and miss engine from solid cast iron bar with the idea of leaving it a couple of thou undersize then hone it to size but the the bar seemed to relieve itself in the process and went out of round about 0.003” so i lapped it instead . It is now round and parallel , the main problem with honing is bellmouthing the cylinder or ending up with a barrel shape as you have no feel with a hone . With a lap you can feel the tight spots and the lap will bring an oval cylinder back into round where a hone won’t . I have decided where possible to stick with a 40mm bore size because i can buy pistons and rings from a 50cc minibike for a few dollars - that is if I don’t feel like making my own of course ! I recently picked up a 39.96mm reamer so i can bore it out close to size and ream it to size then hone or lap the last few thou out easily .
Have a look at robrenz channel on youtube , he makes some laps for larger cylinders that i though worked well enough to copy and use in my smaller cylinders.
I think the next time i make a cylinder liner I will machine it within a few MM or 1/8 inch or so of final size then heat it up to dull red and let it cool slowly to stress relieve it before machining to final size .

 

[goldstar31]

I fully agree with XD351 but the situation goes rather deeper.
The fact that cast iron is unstable obliges people like machine tool manufacturers to buy in castings and rough machine them. They are then put out to 'weather' outside - to grow and distort normally. They are then brought back in for machining and then sold. Unfortunately, this is a very costly 'tie up of money' and with high rates of bank interest it often means the demise of an otherwise viable business. Somewhere in my safe is quite a number of North East share certificates of this. Not mine, I hasten to add but 'family'.

Some years ago I picked up a rather large heavily worn and corroded measuring table top of Meehanite which far more stable-- for the princely sum of £3.
Those years of 'Business Studies' were amply repaid again and again.
The hard job was cutting it up into useful sections--------and the dirt!

N

 

[rsholl]

Sunnen Hone is what you need. Look for an auto engine rebuild shop. If they do any rod work they should have the 1.5" mandrel and stones. I owned a small engine repair shop for over 15 years and rebuilt all types of small engines. I have 3 sets of Sunnen hones to cover from about 1.750"to 6.00" engine bores. This type of hone is the only way to guarantee it will be truly round when you get done. .003 is on the high limit but very doable as cast iron hones very nice. I also grind the OD of the piston rings I make. Grind ring od to size and hone cylinder means no break in.

 

[goldstar31]

Can you let us know what conclusions which you came to about Hoffman's suggestions?

 

[rsholl]

goldstar31, I did check out Hoffman's site and his info on the 1660 Sunnen Hone. I am a tool & die maker by trade and we had a smaller hone which we used to finish hone the ID of our draw dies. I worked in a flash light factory and did my apprentice ship there. Hoffman is spot on and a hone of that type is capable of those kind of tolerances. I also have acquired a similar hone and have bought most of my supplies from ebay. I have found many good mandrels on ebay and stones can be bought from an engine rebuild shop. I am not concerned with .0001 tolerances but rather the ability to get a true and round surface with this tool. A set of 240-320 grit stones for any of the mandrel sizes will give excellent result for a cylinder bore. I prefer to bore to within .0015/.002 of finish size and generally, it will take less than 5 minutes to finish size the part. Patience is the key here. If you get carried away with the hone you can find you are over size very quickly. I tried to attach a photo of the hones I used when rebuilding small engines like B&S, Tecumseh, and Kohler. I have not had a lot of time to build engines in the past 3 years but plan on getting started this winter so the horizontal hone will definitely get a work out.

 

[Naiveambition]

I also read thru Hoffmann site and was really liking the vertical shear tool.
I also liked the puck setup for ease of resharpening. The process seems very similar to honing engraving tools. I had never thought to combine the two.
In Hoffmann site I also noticed he was keen on the tanginetial ( spelling?) cutters for ease of touch ups. Only downside for me was that the tools are ground like the old Southbend tools. And coming from a blank hss would be a lot of grinding to suit this shape. I think it may have been for threading, but could be wrong.
I will try the first tool he described, this one seems easy enough to grind and makes much sense for ease of cuts.
As of now I have a 1.5 inch thru hole brass lap and the flex hone on its way. Thinking is to hone to size then run flex hone thru for cross hatching. Will post my finding.
On a side note cost for tooling was about. 80$ give or take, and when looking for outsourcing I can have it done for 20$ a bore. I chose the other way so I could ensure they weren't just deglazing the cylinder and call it honing. I agree that the sunnen hone would be best suited for this job.
Though the good thing about building theses models is that people are often impressed with what you are doing and will sometimes give you the work for free just for the coolness factor.

 

[goldstar31]

Actually, this Hoffman thing is actually the Goniostat- resurrected and once beloved of Jacob Holzapffel and subsequent Ornamental Turners. The Goniostat, of course, was capable of honing at different angles.
I think the crude one using a child's plastic protractor, a couple vof 'domes of silence' and a bit of square bare is no longer on the 'net- which is a pity. I have it on file for curiosity.

Of course the goniostat was used with-- walrus hide. But that is quite another topic.

N

 

[goldstar31]

I've had a little more time to digest NA's questions.
The first point is that Hoffman's jig seems to be designed to cut 60 degree threads in screwcutting whereas my suggestions about this Goniostat has/had wider choices of angles.

The next point to discuss is rough grinding. OK, I have an arse-nal of tool and cuttery but failing this, I would use the periphery of a grinder to rough out the desired angles.
Assuming that the worktable of a cheap grinder is flat, the height can be packed up with plywood or something to get the desired angle with a fairly simple maths formula as follows:-

The constant os 0.0088 and the wheel in inches and the angle desired.

So it goes:- I want 7 degrees in this case and my wheel is 6"

so it is 0.0088 times 7 times 6 and the resultant answer of 0.3696" has to be approx 3/8th bit of ply.

This is the time that old farts like me used their 'guessing sticks/sliderules' to crunch figures which they could actually achieve.

Does this help?

Norman

I should add - front the centre/center of the wheel

 

[Brian Rupnow]

I have built 30 engines. They all run, some from rather iffy thru to some that are outstanding. I drill the cylinder out to approximately 0.020" undersize. Then using low speed and lots of cutting oil I ream thru with an "on size" reamer. . Then I use a 3 stone brake hone at moderate speed to remove any finish marks left from machining and reaming. And NEVER NEVER let the 3 stone brake hone come out of either end of the cylinder by more than half an inch. Then I use an expanding lap with 600 grit aluminum oxide paste to put the finishing touch on the inside of the cylinder. Then I make the piston to fit the cylinder (actually about .002" less than the finished bore). I use viton O-rings for piston rings.