How to correctly bore out a pulley?

Bearings/Motors/Belts/Gears/Etc.

How to correctly bore out a pulley?

Postby gavztheouch » Thu May 17, 2012 8:24 am

I have a need to bore some pulleys out to various sizes. I recently acquired a little Myford lathe to help me out. Practising on some steel rod the closest to 10mm I can achieve with a twist drill is 10.15mm, really I would like this as close to 10mm as possible as my shaft is 9.98mm. I have a small boring bar which might just scrape in there, but I also need a 6mm bored in another pulley and there is now way my boring bar will fit in there. For the 6mm I have bought a 6mm hand reamer, I plan on centring the pulley in the 3 possible 4 jaw chuck and check with DTI for alignment . Then I will drill to 5.5mm which will prob end up at 5.6 or 5.7mm the use the reamer steadying with the tailstock and manually spinning the chuck.

Anyone else bored pulleys and what is your techniques?

All the best

Gav
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Re: How to correctly bore out a pulley?

Postby iGull » Sun Jun 17, 2012 9:32 pm

Hi Gav

I'm surprised no-one has replied to your question!

OK on the Myford, lucky you, better than most of the chinese garbiage available (like mine) :D

There are a pile of ways to do this, here's what I do.

Let's say you want to drill 10mm exactly (actually, exactly is a waste of time, unless the shaft you have is under 10mm by about 10uM).

I normally chuck up the item in the three jaw chuck (four jaw won't centre easily) - do it a couple of times and check by eye that it is running true (your eye is really accurate). Using a centre drill in the (previously accurately centred) tailstock, drill the centre out.
Using an undersized drill in said tailstock (normal size will generally give an oversized hole) - say 9.8mm (you can buy drills in 0.1mm increments, see Axminster etc) - drill out the hub.
Using an accurate 10mm reamer in the tailstock, you have a couple of options - turn the chuck by hand while winding in the tailstock (preferred) or spool up the chuck and use the tailstock like a drill (bodger's method ).

There are a pile of other variables, speed/feed/lubrication that you need to take in to consideration. Of course, you could just drill it undersized then go the next size up :-)

I would first suggest getting a copy of Tubal Cain's series on lathe work - ancient, but good practical information if you have never used a lathe properly (me neither :D )

Cheers

Neil
EMOs are a sign of weakness ...
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Re: How to correctly bore out a pulley?

Postby daveczrn » Mon Jun 18, 2012 6:16 am

Use saliva to lubricate the reamer. Might just be enough to get a 10mm reamer to cut 9.98mm. I would test this on a similar piece of metal to see what it should cut. Always test before you ruin a part.
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Re: How to correctly bore out a pulley?

Postby Techgraphix » Mon Jun 18, 2012 7:57 am

If you have a lathe, why don't you turn it to the exact size, that is for the 10mm. I did about 20 pulley's this way and all in a three jaw chuck.
If you pre-drill the 6mm holes with 5.7 then 5.9 and finaly with a 6mm endmill, i'm sure you will end within tolerance.

Kees
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Re: How to correctly bore out a pulley?

Postby macona » Mon Jun 18, 2012 9:09 am

The proper way? First you must understand that drilling is one of the most inaccurate ways of making a hole. Standard twist drills rarely cut to size and are almost never straight.

Drill undersize. Do not use a center drill! Center drills are for dead/live centers. The tapered hole will cause the bit to grab and start off center giving a wobbly. Either use a spotting drill to make a spot or a screw machine length drill. Split point is even better.

After drilling use a small boring bar to bring the hole to the correct diameter. If you really need a good finish then bore undersize and use a reamer. In steel I recommend high sulphur cutting oil. Lubricating oils are no good for cutting.

If you need to be as accurate as possible, use a 4 jaw. 3 jaws are only good for rough work or situations where the stock is never removed. Once you get the hang of it you can set a 4 jaw in a couple minutes to sub thou levels.

They do make small boring bars. You can also grind your own out of a old end mill.
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Re: How to correctly bore out a pulley?

Postby iGull » Mon Jun 18, 2012 8:25 pm

LOL, it's amazing what happens when you reply to a thread :D :D :D :D

All the real engineers suddenly pop out :D :D :D :D

Cheers

Neil
EMOs are a sign of weakness ...
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Re: How to correctly bore out a pulley?

Postby macona » Tue Jun 19, 2012 9:34 am

Engineer? Are you trying to insult me??? ;)

More like machinist.

-Jerry
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Re: How to correctly bore out a pulley?

Postby Enraged » Tue Jun 19, 2012 6:48 pm

macona wrote:Engineer? Are you trying to insult me??? ;)


Ha, made me chuckle

/not an engineer, just a lowly technologist
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Re: How to correctly bore out a pulley?

Postby Cre8ivdsgn » Sun Jul 29, 2012 5:11 pm

People are going to scream at me for this method, but what the heck:
1) I once made multiple sets of aluminum jaw replacements for my kurt vice. (This is a helpful thing in general.)
2) I took a set and bored a hole (with the jaws tight together) that matched the pulley diameter across the teeth.
2a) If there is a flange, you need to back bore the jaws to provide clearance before you do the hole that grabs the tooth diameter. Or remove the flange.
3) Drop in a pulley and use a boring bar to get the diameter you want.

This method results in excellent parallel placement of the new hole to the teeth of the pulley.

Later, when boring a new hole diameter for the same size pulley, I use a Blake Coax indicator to find the center again.

BUT - I have good glass scales on my mill and my mill is in good shape. And the lathe I have access to is an old beater that I wouldn't trust with anything.

Safety tip - the boring bar is typically longer than most other tools. Make sure (knee mill or otherwise) that you have plenty of clearance for all tools before starting this!

(I'll have to wear a bag over my head for even mentioning this technique, but I figure that others have to contend with this mod without the benefit of a lathe...)
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Re: How to correctly bore out a pulley?

Postby joskerel » Mon Jul 30, 2012 1:58 pm

Use saliva to lubricate the reamer


Or your Brainwaves :mrgreen: :mrgreen: :mrgreen:
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