Line boring bar idea

[xander janssen]

Hi all,

After building several Stirling engines and Jan Ridders (like) IC engine, I'm thinking of designing my own 2 or 3 or 4 cylinder IC engine loosely based on the appearance of the BruceMacBeth engine.

Idea is to use a build cranckshaft with oversized journals that include ball-bearings like: German example of a build crankshaft

This because I tried this technique before and its construction works well with the machines (lathe, mill) that I have. Whereas fully turned or brazed crankshafts never turned out very well.

To incorporate this crankshaft, I need to perform a line-boring operation on the crankhousing made from aluminum.

I would like to get you opnion on the following idea for a line boring bar that can be used on the lathe between centers, with the crankcasing situated on the carriage.

Diameter of the bar: 30 mm
Diameter of final bore: 37 mm

 

[ICEpeter]

Hello Xander,
I have made such a line boring bar myself a while ago for the same purpose for use between centers in a lathe. Myford in the UK I believe has them as well as an accessory for sale. Making one is not too difficult provided you have or have access to a square reamer of the size of your cutting insert.
I suggest to google "line boring bar" and you will get some hits.

Peter J.

 

[xander janssen]

I do not have a square broach. That is why I want to use a round toolbit with a flat on it. I hope this will work well for very light cuts.

 

[ICEpeter]

I do not have a square broach. That is why I want to use a round toolbit with a flat on it. I hope this will work well for very light cuts.

If you do not have a square broach, do it the old fashion way and file the round hole square to fit the size of your tool bit which I assume, based on the diameter of your bar, could be 3/16 or 1/4 inch which would accommodate filing a square hole quite easily.
Since you provide your dimensions in Millimeters, are you located in Europe somewhere or elsewhere?

Peter J.

 

[Jasonb]

Should work fine, I've a couple like that. Another option with the tool bit is to drill a hole to suit the across corners size of say 3/16 or 1/4 square toolsteel. I mostly just use round HSS though. The bar in these videos is 28mm so not far off your proposed size

 

[BaronJ]

Should work fine, I've a couple like that. Another option with the tool bit is to drill a hole to suit the across corners size of say 3/16 or 1/4 square toolsteel. I mostly just use round HSS though. The bar in these videos is 28mm so not far off your proposed size

Yes, that is what I do as well, a round hole and a pinch screw. Even using round HSS I grind a flat for the pinch screw to bite onto.

One dodge that I also use is a grub screw underneath to push the tool bit out a bit. Which also allows you to use a mic to set the amount of cut.

 

[xander janssen]

Thanks for your replies. Make me more confident to give it a try.

Indeed, I live in Europe. Belgium to be more precise. Pretty used to the metric system indeed

 

[SmithDoor]

I just ground stock or O1 or W1 drill rod
The drill a hole for cutting tool and drill & tap to hold the cutting tool.
You buy round tool bits or use a old end mill.

Dave

Thanks for your replies. Make me more confident to give it a try.

Indeed, I live in Europe. Belgium to be more precise. Pretty used to the metric system indeed

 

[tonyr769]

You can use an old tool making dodge to make a square hole. Drill a hole just on size and file it out nearly to the square size. Then grind the hss tool bit square at the ends. One end with sharp corners. Then tap the hss tool through the hole similar to a broach. When a burr is raised at the working edge gently file burr down and tap drift through again. You can get a very accurate and secure square hole this way. Take care and use safety glasses as the hss tool bit may shatter if hit too hard. I would then use a new bit for cutting as cracks may have been introduced to the working bit.
May be of use.

Tony

 

[BaronJ]

You can use an old tool making dodge to make a square hole. Drill a hole just on size and file it out nearly to the square size. Then grind the hss tool bit square at the ends. One end with sharp corners. Then tap the hss tool through the hole similar to a broach. When a burr is raised at the working edge gently file burr down and tap drift through again. You can get a very accurate and secure square hole this way. Take care and use safety glasses as the hss tool bit may shatter if hit too hard. I would then use a new bit for cutting as cracks may have been introduced to the working bit.
May be of use.

Tony

Hi Tony,
Have a look at this thread,
https://www.homemodelenginemachinist.com/threads/cutter-grinder.32385/page-2#post-345645

 

[tonyr769]

Hi Tony,
Have a look at this thread,
https://www.homemodelenginemachinist.com/threads/cutter-grinder.32385/page-2#post-345645

Hi Baron,

I thought that was an ingenious idea for cutting a key slot. The method I mentioned is used for a hole at right angles to the boring bar.

Tony

 

[deverett]

If you enjoy tool making, you might like to copy G.H. Thomas' between centre boring bar design.
Basically, he uses a round toolbit set over at 45 deg and uses a 40 tpi screw to advance it. A lock screw prevents unwanted movement.
I can send you details if you would like.

Dave
The Emerald Isle

 

[goldstar31]

Dave
Might I add a small correction? The angle to compensate is actually 40 degrees which gives an amost correct cut using 40TPI.

Well that is what I made when boring the two bed bars on the Mark1 Quorn tool and cutter grinder which has to hit 1.000" on the castings apart from one at 1.003" if one is not using split cotters 'wot I did'

Best wishes. Great book for £30-ish

Norman

 

[ignator]

There's a youtube channel I watch, a repair machinist, that shows the making of a large line boring bar that may be of interest to his technique and usage:
3 part series

 

[BaronJ]

Hi Baron,

I thought that was an ingenious idea for cutting a key slot. The method I mentioned is used for a hole at right angles to the boring bar.

Tony

Hi Tony
Thanks for your comments.

You could use exactly the same Idea on a round, square or rectangular bar to make a square hole through it. My broach will work just as well using a square section as it will in a between centers line boring bar to produce a round hole.

Obviously it gets harder as things get smaller, my original key slot cutter was for a 4 mm keyway in steel pulleys.

 

[tonyr769]

If you enjoy tool making, you might like to copy G.H. Thomas' between centre boring bar design.
Basically, he uses a round toolbit set over at 45 deg and uses a 40 tpi screw to advance it. A lock screw prevents unwanted movement.
I can send you details if you would like
Dave
The Emerald Isle

Hi Dave

Not sure if your message was for me or the author. Anyway I personally do enjoy tool making having trained as a press tool tool maker. Thanks for your offer but G H Thomas' book is on my Christmas wish list.

Thanks
Tony

 

[goldstar31]

Hi Dave

Not sure if your message was for me or the author. Anyway I personally do enjoy tool making having trained as a press tool tool maker. Thanks for your offer but G H Thomas' book is on my Christmas wish list.

Thanks
Tony

Get BOTH books as I did. His Workshop Techniques is also a fine read

 

[Steamchick]

Nice to see boring the way I was taught in the 1960s... "Transcribe a circle then pass it through the workpiece to get a "perfect" cylinder" as my Father taught me... I made a few boring bars in my teens for various jobs... still have some and use for cylinders. Also use in the Miller for vertically boring cylinder blocks and sets of aligned plumber blocks. (Or are they Plummer blocks? - After a chap of that name?). This method simulated dedicated Boring bars for engine blocks, etc.
K

 

[Gordon]

Apparently I am missing something on G H Thomas books. I am not familiar with them so I looked on Amazon and the price is $218. They would have to be pretty spectacular at that price. Are the books available somewhere at a reasonable price?

 

[L98fiero]

Apparently I am missing something on G H Thomas books. I am not familiar with them so I looked on Amazon and the price is $218. They would have to be pretty spectacular at that price. Are the books available somewhere at a reasonable price?

Tee Publishing £27 https://www.teepublishing.co.uk/books/in-your-workshop/workshop-techniques/
Tee Publishing £27 https://www.teepublishing.co.uk/books/in-your-workshop/model-engineers-workshop-manual/