boring a taper-- starting with a 0.275 (7mm) bore

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sierrasmith71
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Joined: Wed Mar 22, 2017 8:09 pm

boring a taper-- starting with a 0.275 (7mm) bore

Post by sierrasmith71 »

FOkks.

I need to make a flywheel that the dwg. shows a center bore with a 10 degree (included angle) taper that ends in a bore diameter of 7mm (0.275").
Depth of the hub is 15mm (0.591")

Ok, so I start with a 7mm drilled hole. but what tool can I use to turn the taper. I don't have any boring tools small enough to fit inside the 7mm opening. Nor can I seem to find one anywhere...Any ideas???


Thanks in advance

David G.
John Evans
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by John Evans »

You arn't looking hard enough ! LOL In my tooling collection I have HSS that will bore 1/8" and Micro 1000 solid carbide 1/8 shank that will do not much bigger,also insert style 1/4 shank Circle brand that would work. You should be able to grind a bar out of a 1/4 sq HSS piece.
www.chaski.com
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Harold_V
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by Harold_V »

As John said, you should be able to hand grind the tool you need. It's all very much a part of running manual lathes. It would have been very unusual for a machinist to seek such a bar in my day---it was rarely a purchased item.

If you are not adept at grinding turning tools, I highly recommend you pursue the art. Once mastered, there's little you can't do with hand ground tools, avoiding the waiting period you often experience when trying to buy what you can make.

Welcome to the board!

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
Magicniner
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by Magicniner »

Whilst learning to grind your own HSS tools you might also search for "micro boring bar lathe" on the usual auction sites.
I picked up a slack handfull of carbide micro boring bars for £20, a mix of 3mm and 4mm shanks they were all used but touched up nicely on a diamond wheel, that allows me to spend the time saved making the part I wanted the boring bar for ;-)

- Nick
John Hasler
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by John Hasler »

sierrasmith71 wrote:FOkks.

I need to make a flywheel that the dwg. shows a center bore with a 10 degree (included angle) taper that ends in a bore diameter of 7mm (0.275").
Depth of the hub is 15mm (0.591")

Ok, so I start with a 7mm drilled hole. but what tool can I use to turn the taper. I don't have any boring tools small enough to fit inside the 7mm opening. Nor can I seem to find one anywhere...Any ideas???


Thanks in advance

David G.
Best to grind one from .25" round HSS but for this you can use a 1/4" HSS stub drill bit. For a taper you need no backrelief.
Rich_Carlstedt
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by Rich_Carlstedt »

Set your Tool slide to the 5 Degree angle
Mount a 1/4 endmill in your tool holder and set it to be perfectly parallel to the spindle axis.
make sure that one flute nearest you is at center height .
Take a roughing cut by plunging in using your tool slide only .
When you are real close to size, stop spindle turning and extend the tool slide and then touch the endmill to your bore at the back.
Now start the spindle and draw the endmill out and you should get a smooth cut that is on size related to the bore bottom
Using a 1/4 endmill ( .250) means you should not accidentally make the hole oversize ( .270)
If you have a radiused endmill, you will get a smoother cut, but it is easier to go oversize.

Rich
stephenc
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by stephenc »

So far in my career as a hobby machinist I haven't had to cut any small diameter tapers like the op .
And that brings up a question I have .. for those of us who don't happen to have boring bars on hand small enough to fit in such a small hole , why not just make a reamer?

To my thinking a reamer just makes more sense . It gives you the opportunity to be absolutely sure you have the taper correct before working on the part and d bit style reamers are cheAp and easy to make .

Even if I had a bar small enough for the hole I would still be likely to make a reamer to do the job simply because I think I would get a more accurate taper with a better finish then using a boring bar .

But my thinking is often flawed due to a lack of experience though .... If I am way off base I'd like to be put on the right path
Rich_Carlstedt
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by Rich_Carlstedt »

No Stephen you are not off base .
David could make a "D" bit quite easily and at the same time, use the same cutter and setup to turn his crankshaft for the match taper.
Making D bits from drill rod is not difficult, but it does take some time to do the job.
There are many ways to skin a cat as they say , and it is never more true than in machining .
The decision on which method lies in several areas.
1. Material on hand
2. Tools on hand
3. Time available or needed
4. Skills required
5. Cost of doing it
Any of the above 5 can cause a change in procedure or method
You may also add "experience" as a factor.
I have known many machinists that had the tools and materials but selected the method they used before as they felt more comfortable even though they had access to the " latest and greatest " !

Rich
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Harold_V
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by Harold_V »

A reamer for a tapered hole can be troublesome, especially if powered. The problem comes from the amount of tool in contact with the cut, the lesson most of us learn when we try to use form tools when turning. It often results in a chatter finish, and may or may not result in a truly round cut, as reamers are notorious for providing multi-sided holes. Bottom line---one has far greater control over the end result using a boring bar than might be expected from a reamer, depending on the application. This is an excellent example of where a boring bar would be superior.

Boring small holes can be taxing, but I've enjoyed success boring a 1/16" diameter hole, hand grinding the tool from a broken drill shank. Boring one as large as the one in question shouldn't be difficult.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.
sierrasmith71
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Joined: Wed Mar 22, 2017 8:09 pm

Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by sierrasmith71 »

Set your Tool slide to the 5 Degree angle
Mount a 1/4 endmill in your tool holder and set it to be perfectly parallel to the spindle axis.
make sure that one flute nearest you is at center height .
Take a roughing cut by plunging in using your tool slide only .
When you are real close to size, stop spindle turning and extend the tool slide and then touch the endmill to your bore at the back.
Now start the spindle and draw the endmill out and you should get a smooth cut that is on size related to the bore bottom
Using a 1/4 endmill ( .250) means you should not accidentally make the hole oversize ( .270)
If you have a radiused endmill, you will get a smoother cut, but it is easier to go oversize.
This is quite an intriguing idea! I will try it (on a scrap piece first) in the next few days and let everyone know my results.

Thanks the many responses to my inquiry. I was aware that grinding a tool bit was probably the way to go , but I have yet to add grinding bits to my arsenal of skills that I am rapidly building.

Best to all

David G.
earlgo
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by earlgo »

Harold: I do not have anywhere near your experience so I have to believe your comments about reamers.
Having said that, I have never had a "D" style reamer chatter. The last one I made was for a sizing die for a .218 Mashburn Bee, and the result was a smooth finish that just required a little touchup with emery cloth.
Reaming the sizing die a.jpg
I guess that I was just lucky.
--earlgo
Before you do anything, you must do something else first. - Washington's principle.
earlgo
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Re: boring a taper-- starting with a 0.275 (7mm) bore

Post by earlgo »

Before anyone asks, the reamer is below centerline because it is being held by a floating reamer holder that prevents rotation but allows the reamer to follow the axis of rotation. Very helpful to prevent 'bell-mouth'.

--earlgo
Before you do anything, you must do something else first. - Washington's principle.
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