PM Research #5 - how do I bore the main crankshaft journals?

[nz120]

Hi

After 15 years break with kids I have pulled out an old half-built PM Research #5 kit and have been making good progress.
I'm now at the point of needing to bore the main journals for the crankshaft.

I can't work out how to bore a .313 hole on each bearing AND make sure that they are in line.

I am using a Sherline lathe and mill, and have a adjustable boring head that takes the 3/8" boring tool. But this of course is very short for that small diameter boring tool so I can't just start boring on one side and go through the full width of the casting and continue to bore the second journal from behind.

Having skimmed the casting I'm confident that I have the same height to the centre of each journal point, but I can see that no matter how carefully I try to square up the casting before boring each journal individually that I can't guarantee that the two bores will be in perfect alignment.

Any suggestions welcome.

regards
Andrew
Auckland
New Zealand

 

[vederstein]

I think when I did mine, I reamed a hole all the way through. It's been many years since then, perhaps I forgot.

 

[nz120]

I think when I did mine, I reamed a hole all the way through. It's been many years since then, perhaps I forgot.

Thank you for the prompt response.
So do you mean that you used a REAMER, rather than a boring bit?
I see that there are 5/16" reamers available.....do you suggest drilling a pilot hole right through both journals then reaming through from one side through both journals?

 

[vederstein]

If I remember correctly, I think that's how I did it. But my equipment is considerably larger than a Sherline.

 

[davidyat]

I agree with Vederstein. When I did mine years ago, I drilled a pilot hole, used a 19/64 drill to open it up and finished with a 5/16 reamer. Then turned the crank ends as close as I could to 5/16. I like to get tolerances extremely close to finish so that when I assemble the crank into the bearing housing, it's a really snug fit. Then I take off the bearing caps, smear a little lapping compound, and start to snug down the bearing caps while slowly turning the crank chucked up in my cordless drill. Just keep turning, snugging down the caps till tight. Then remove the lapping compound, put a little oil on the bearings and see if you can turn the crank by hand. If not, repeat lapping till you can.
Grasshopper

 

[Shopgeezer]

For a multi cylinder engine the right way is to line bore the engine block. The video below shows the idea. He is holding the bore in a three jaw chuck. It should be between centres. Packing the block to the correct height would be challenging. For a single cylinder engine the drill and ream technique is much simpler.

 

[nz120]

For a multi cylinder engine the right way is to line bore the engine block. The video below shows the idea. He is holding the bore in a three jaw chuck. It should be between centres. Packing the block to the correct height would be challenging. For a single cylinder engine the drill and ream technique is much simpler.

Thanks for that post....that makes sense. Not sure that my skills are up to making a boring bar small enough for a 5/16" bore, but I'll retain that information for when I need something bigger.

 

[nz120]

I agree with Vederstein. When I did mine years ago, I drilled a pilot hole, used a 19/64 drill to open it up and finished with a 5/16 reamer. Then turned the crank ends as close as I could to 5/16. I like to get tolerances extremely close to finish so that when I assemble the crank into the bearing housing, it's a really snug fit. Then I take off the bearing caps, smear a little lapping compound, and start to snug down the bearing caps while slowly turning the crank chucked up in my cordless drill. Just keep turning, snugging down the caps till tight. Then remove the lapping compound, put a little oil on the bearings and see if you can turn the crank by hand. If not, repeat lapping till you can.
Grasshopper

Thank you for the confirmation....have ordered the 19/64 drill and 5/16 reamer and will await the courier

 

[kwoodhands]

Thanks for that post....that makes sense. Not sure that my skills are up to making a boring bar small enough for a 5/16" bore, but I'll retain that information for when I need something bigger.

Make your small boring bars from Allen wrenches. The steel is very hard. I use a Dremel tool and cut off wheel to reduce the short leg to a length needed. Even the front relief can be roughly done with a Dremel tool.
mike

 

[nz120]

Make your small boring bars from Allen wrenches. The steel is very hard. I use a Dremel tool and cut off wheel to reduce the short leg to a length needed. Even the front relief can be roughly done with a Dremel tool.
mike

Mike, great tip...will try that....I take it that you just sharpen the actual Allen wrench to a cutting edge....

 

[kwoodhands]

Mike, great tip...will try that....I take it that you just sharpen the actual Allen wrench to a cutting edge....

I usually grind the front relief 10°. Side rake and back rake about 15°. Different materials call for different angles. I usually just use the same ones for every metal. It is rare that I have to bore smaller bores .
Little Machine Shop has an informative article on grinding HSS lathe cutters.
I do not grind side relief, not needed in a boring tool.
mike

 

[Steamchick]

I agree with the "line-boring" explanation shown above by Shopgeezer. - EXACTLY as I did my Sirius main bearings. The Engineering is that a Boring tool driven by the lathe (or equivalent) is describing an exact circle. - which then transposes along the length of the item being machined. Actually, reamers generate a series of curves (a bit like the outside of a 50p piece). - There are 1 more arcs than the number of flutes on the reamer. These arcs form a very good circle, but not a perfect circle. To honing is better. Also an off-alignment reamer, or hone can give tapers in the bores.... just as the simple mounting of a part in the lathe and tool in tool post can produce a taper of the finest of mis-alignments of the bed to chuck, or due to tool cutting pressure causing distortion.. or movement of the main slide..... So the Boring Bar is best!
Enjoy.

 

[Steamchick]

Hi Andrew, You could make the boring bar from 1/4" silver steel, with a small cutter fitted into a hole in the middle of the shaft. - Grind to an edge after securing the tool bit. The smallest tool I have is made from 1/8" round tool steel sweated into a piece of steel using a lead solder - to avoid hardening and tempering problems. Or you can braze on a chip from a broken sintered tool bit, masonry drill, or other hard steel. But I like the Allen key as a source of suitable steel for the boring tool. - I also use old files...

 

[Steamchick]

What I didn't mention, was that in grinding the tool to size, you need to measure, with a good micrometer, from the tip of the tool to the reverse side of the bar - then do the maths to calculate the radius that is on the tool, from the centre-line of the bar. I'm struggling to put into words what is easily explained in a picture, but I'm sure you can work it out anyway.

 

[BaronJ]

Hi Guys,

You need need to make a small adjuster to push the cutter tip forward accurately.

I designed this tool to fit over the boring bar and push it forward by an exact amount. The calibrated alloy knob is marked in 1 thou increments.

The largest diameter bar that can be adjusted is 20 mm and the smallest is 6 mm, maybe 5 mm at a stretch.

 

[goldstar31]

I have two in line boring bars( somewhere) to George Thomas's instructions in Model Engineers Workshop which has the cutting tool angled so that the internal manual tool locking rod can be pushed to project exactkky in thous using a 1/4 40TPI ME thread.

OK, that's me but if this is not done for any reason, the tail stock can be adjusted and will bore perfectly parallel.
If one has a boring head which adjusts, the normal tool can be substituted with a tool shaped as a centre.

Again, a similar boring head can do ball handles.

Quite intersting really

Norman

 

[Shopgeezer]

I would love to see a diagram or photo of this gadget. An adjustable line boring bar would be very convenient.

 

[goldstar31]

I would love to see a diagram or photo of this gadget. An adjustable line boring bar would be very convenient.

George Thomas was one of these pedantic perfectionists and not for everyone.

I bought my first copy of 'Model Engineer's Workshop Manual' after buying the two earlier books 'The Universal Pillar Tool' and Dividing and Graduating' Thesse two books were amalgamated in Thomas's' Workshop Techniques' as a posthumous tribute to him.

Not for everyone but if you are contemplating something like Professor Dennis Chaddock's Quorn tool and cutter grinder, these two books are excellent.

 

[nz120]

I do appreciate all your comments, and pleased that my initial problem has raised a number of helpful suggestions. Given that the PMR #5 is my first attempt at parallel bearings, and that I doubt if my overall precision is perfect anyway I intend to drill and ream and see how I go.

I actually have two complete PMR #5 kits (about year 2000 vintage) one of which I am building and the other unopened. I am using the first as a learning exercise and can then
embark (time allowing) on the second with all the things I have learned.

Today I have found the limitations in size of the Sherline mill which does not have the height to drill if I mount the main casting upright on the rotary table. Everything is a challenge and a learning opportunity

 

[BaronJ]

Hi Nz120, I'm curious as to why you are using a rotary table ?