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Old 12-10-2019, 05:13 PM   #1
Mart
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Default Specific questions re using a boring bar (Old school)

Hi fellas.

I've been testing my boring bar and have a few questions. I would appreciate any advice you can offer. I've set it up on an otherwise scrap block and have been taking some test cuts.

1,I'm boring to suit some used pistons. They are +60s and measure 3.246. What would my target bore be after honing? Is it 1 thou per inch so lets say 3.249?

2, How many thou do you allow for when honing? 1? Or hardly anything?

3, When fitting sleeves, how much do you leave at the bottom of the bore for the sleeve to sit on?

4, When the cutting tool reaches the bottom of the bore, do you then somehow withdraw or remove the tool before bringing the bar back up to the top of the bore? (To save putting a scratch up the bore.)

5, what diameter and thread is used in general for the clamping mechanism? I have made two clamps using 12mm threaded rod. I think it looks pretty strong but wondered what the pukka setups use. Is one clamp normal, or are two used sometimes?

I'm getting closer to actually trying to do this for real so would appreciate any help that can be offered.

Thanks in advance.

Mart.
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Old 12-10-2019, 05:16 PM   #2
Kurt in NJ
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Default Re: Specific questions re using a boring bar (Old school)

What brand and model boring bar
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Old 12-10-2019, 05:29 PM   #3
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Default Re: Specific questions re using a boring bar (Old school)

The boresize is your startingpoint...the pistons are made as much undersize as they need to be for clearance....compensating for a used piston is a gamble...donīt go much under the +.060.

How much you leave for honing depends on how good the bar is...check for taper and acuracy between cuts...in a perfect world handhoning you would like to do 10 strokes and be done...

You donīt need much for keeping the sleeve in place my rule is the lip should not be less then square...so depth of cut long atleast.

The scratch from toolbit returning shouldnīt be much on the last cut ( should be light enough so the bar doesnīt flex).

You need some clamps for the bar i have them here...yours for the shipping cost.

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Old 12-10-2019, 05:43 PM   #4
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Default Re: Specific questions re using a boring bar (Old school)

Thanks Murre. I've made some clamps, no need to worry about sending some, but thanks for thinking about it.

It's a vintage Buma machine, probably from the 1930s or 40s.

Understand re the lip for the sleeve.

Lets say I'm going from 30 thou to 60 thou, would you expect that to be done in one step or two?

Is there a minimum cut you can take? Or is it difficult to cut a very small amount and hard to arrive at a size. If using two steps to arrive at a size should the two steps be even? or in this case say go to +50 then ten more to +60?

I suppose it is very much a case of learning the individual machine.

Thanks for the help.

Mart.
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Old 12-10-2019, 05:58 PM   #5
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Default Re: Specific questions re using a boring bar (Old school)

First the cutting bit is usually one rough and one fine cut version with different grinding on the older bars.
If you get the geometry of the bit wrong you get shatter.

You can take the roughcuts as tough as the bar handles without protesting...i woudnīt try a to heavy cut since youīre not in a hurry.

Then you go down to a real light finish cut for acuracy in the end.

No minimum cut, i wouldnīt go more then 20 in a single pass...and since youīre not in a great hurry...a few more passes and acuracy for less honing is better...
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Old 12-10-2019, 06:14 PM   #6
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Default Re: Specific questions re using a boring bar (Old school)

Quote:
Originally Posted by Mart View Post
Hi fellas.

I've been testing my boring bar and have a few questions. I would appreciate any advice you can offer. I've set it up on an otherwise scrap block and have been taking some test cuts.

1,I'm boring to suit some used pistons. They are +60s and measure 3.246. What would my target bore be after honing? Is it 1 thou per inch so lets say 3.249?

2, How many thou do you allow for when honing? 1? Or hardly anything?

3, When fitting sleeves, how much do you leave at the bottom of the bore for the sleeve to sit on?

4, When the cutting tool reaches the bottom of the bore, do you then somehow withdraw or remove the tool before bringing the bar back up to the top of the bore? (To save putting a scratch up the bore.)

5, what diameter and thread is used in general for the clamping mechanism? I have made two clamps using 12mm threaded rod. I think it looks pretty strong but wondered what the pukka setups use. Is one clamp normal, or are two used sometimes?

I'm getting closer to actually trying to do this for real so would appreciate any help that can be offered.

Thanks in advance.

Mart.
Hi Mart, with any deck-mounted bar I would recommend boring the smallest amount of material as possible in one pass. On a +.030" o'bore I would take about .024"/.025" (nominally). For a +.060" o'bore I would consider making 2 passes, etc.!

In order to get an excellent base for the rings to seal you should leave about .005"/.006" to finish hone. We generally leave .006" to hone but we have a power-stroked machine so it's relatively easy for us.

If you're planning on hand-honing (.005".006") to the required size, that much material will be a task!

At the bottom of the bore you want the sleeve to be resting on a "full-round" register, the bar should have some type auto-stop?? Don't worry too much about leaving a "line" from the cutter on the way up, it won't hurt anything!
If I recall, the older deck mounted bar we once used had an "auto-retract" built in?

Thanks, Gary in N.Y.

P.S. We bore all our units on a CNC w/o a block-plate, but we do finish EVERY hole with the block-plate bolted in place. Makes for a "round" hole after the head bolts are installed.
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Old 12-10-2019, 06:21 PM   #7
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Default Re: Specific questions re using a boring bar (Old school)

Thanks Murre.

The tool is home made and uses a small left hand lathe tool modified to fit. It has changeable tips. It cuts pretty well without chattering.

My first test cut was bigger than intended I accidentally went to +105 from +30 in one go! Whoops. The tool coped well, but the motor cut out.

I just went from +30 to +60 in one go. It seemed ok but I have not really measured it properly at multiple points.

I'll try it again in two steps and go 20 then a 10. Does that sound like a better idea? Or maybe 25 then 5?

Thanks for your help.

Edit after reading Gosfast reply:

Yeah, I don't fancy honing 5 thou. I want to hone as little as possible.

I do have an auto switch off so I hope I can use that for the ledge for the sleeve.

No auto retract, but I did manage to remove the tip from the tool as a test to see if that would be one way of doing it.

Please understand I am not trying to build a state of the art flatty, I'm just trying to get that crusty flatty I bought to run. The budget for this little adventure is virtually non existant.

I do appreciate all the input though, knowing how it is supposed to be done is great.

Mart.

Last edited by Mart; 12-10-2019 at 06:33 PM.
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Old 12-10-2019, 07:06 PM   #8
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Default Re: Specific questions re using a boring bar (Old school)

I don't know diddly about old school boring bars but if I needed to know anything about them I'd PM Roseville carl here on the barn. If he can't help you I'm guessing he will know someone who can.
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Old 12-11-2019, 02:44 AM   #9
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Default Re: Specific questions re using a boring bar (Old school)

It all depends on how much the bar flexes...the first Storm bar i ran you had to go very easy on last cut...nowdays i can do it single pass and end up dead on.

I would go 25/3/1 measuring after the 25 and 3 cut to be able to land within 1 for less honing...you donīt want a rough surface or to much material left to hone...and you donīt want to overbore !!!

A heavy cut will give you taper if the bar flex or is loosely adjusted/worn.

When you have got to know your boringbar you should be able to end up withing 1/2thou.

Get a positive small radius finishcut K insert for the cutter preferably coated.
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Old 12-11-2019, 04:18 AM   #10
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Default Re: Specific questions re using a boring bar (Old school)

Thanks Murre, all points noted.

Pics of the business end of the machine and the home made cutting tool:


Attached Images
File Type: jpg cutter.jpg (48.4 KB, 188 views)
File Type: jpg buma.jpg (63.7 KB, 189 views)

Last edited by Mart; 12-11-2019 at 04:31 AM.
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Old 12-11-2019, 07:54 AM   #11
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Default Re: Specific questions re using a boring bar (Old school)

Thanks again for all the advice. I just did some test cuts and was able to get within half a thou of my target bore.

I'm very happy with that and will do a couple more and then try it for real on the proper block.

Thanks again.

Mart.
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Old 12-11-2019, 08:31 AM   #12
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Default Re: Specific questions re using a boring bar (Old school)

"Old school????" What's "New school" ???
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Old 12-12-2019, 12:59 AM   #13
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Default Re: Specific questions re using a boring bar (Old school)

If your hand honing go to .0015 to .002 it will hone up pretty quick.
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Old 12-12-2019, 01:35 PM   #14
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Default Re: Specific questions re using a boring bar (Old school)

Mart, i hope your making another video. I want to see you setup that boring rig and making bigger holes.
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Old 12-12-2019, 03:26 PM   #15
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Default Re: Specific questions re using a boring bar (Old school)

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If your hand honing go to .0015 to .002 it will hone up pretty quick.




I agree works for me perfectly every time no more than .002 if your able to make yourself a torque plate the final results will be even better. The first torque plate I had was simply made from an 8BA head that we resurfaced. I used a big hole saw to cut out the tops of the cylinders this allowed the hone to get to the bores which on that first block was only 3-3/8 plus.030. The iron pile under that block was HUGE. The engine wasn't very good on economy but she sure was fast.
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Old 12-12-2019, 03:28 PM   #16
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Default Re: Specific questions re using a boring bar (Old school)

Thanks Russ. Test bores taking place currently. Videos will be following along.
There will be a new one tomorrow showing the first stage of the prep for the test boring.

Thanks Ronnie. All good points. I hadn't considered a honing plate. If I ever do anything other than trying to get this one motor to run again I will certainly think about it.

Mart.
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Old 12-12-2019, 03:37 PM   #17
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Default Re: Specific questions re using a boring bar (Old school)

This with a Van Norman bar.
I remember cutting about .030 at a pass, sort of max.
Make the last cut a light one, maybe .010. This will keep a straighter bore.
Hand honing, with a good sharp boring bar bit, You hone .001 pretty easily... Leave about .002 so you can get to a solid surface for the rings to seat on.
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