Author Topic: Hard to hold.....  (Read 1391 times)

Offline AdeV

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Hard to hold.....
« on: December 22, 2020, 01:46:44 PM »
I've been asked to do a little boring (or maybe a boring little...) job.... See attached pics for info.

Basically, it's a toothed belt pulley, it'll be used to drive a mechanism. I need to bore the centre hole out to 25mm. Unfortunately, the boss is smaller than that & will disappear, so I can't hold it on that. If I do this in the lathe, it'll have to be held on the outer rims. Couple of issues there: They're really thin, and subject to distortion (it's an aluminium pulley too, so REALLY susceptible to distortion), and the spacing looks like I can't get it to sit on the flats on my chuck, at least one rim will always be at some point on the V-shaped grooved "grips".

My thinking is: Get a couple of bits of plastic, screw them together, bore a hole in the centre to fit the OD of the main pulley surface. Then, somehow, hold the whole thing together & turn the OD round. Split them, put them around the pulley, and in theory I can clamp onto the plastic & have it basically concentric (a few thou runout shouldn't hurt, this isn't a precision mechanism); drill & bore.


...Or, I could put it on the milling machine, and do it that way; I can strap clamp it to the rotary table that's on there now, or just straight onto the bed (well, raised up a bit obvs). and drill/boring head it to size...

Unless there's a crafty trick I'm missing on the lathe?  Let me know!

Cheers!
Ade.


PS: OD is approx 3-1/8", or 78mm for those who speak French.
Cheers!
Ade.
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Offline philf

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Re: Hard to hold.....
« Reply #1 on: December 22, 2020, 02:08:22 PM »
Ade,

The flanges are some times easy to remove.

Alternatively, if you want to grip it in a 3 jaw, cut 3 small lengths of square bar that will fit between the flanges and clamp on the OD of the pulley.

Phil.
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Offline Muzzerboy

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Re: Hard to hold.....
« Reply #2 on: December 22, 2020, 02:15:44 PM »
Get 4 short lengths of round stock with a diameter that is greater than the depth of the flanges and a length just shorter than the inner distance between the flanges. Then tape them onto the outside diameter of the toothed body, with their axes parallel to the pulley bore, ideally 90 degrees apart. Then you can grip them in your 4 jaw chuck and dial them in perfectly while holding them securely without damage.

When setting up, use a DTI to minimise the runout of both the bore and the face.

You could use the same technique with 3 of them and use a 3 jaw chuck but for that you'd need a pulley with teeth that are a multiple of 3. Even so, you are better off with a 4 jaw to minimise any runout.

Offline Brass_Machine

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Re: Hard to hold.....
« Reply #3 on: December 22, 2020, 02:17:34 PM »
...
Alternatively, if you want to grip it in a 3 jaw, cut 3 small lengths of square bar that will fit between the flanges and clamp on the OD of the pulley.

...

I second this. Worked for me. 3 (or 4 if using a 4 jaw) pieces of scrap aluminum that fit between the flanges. I also machined a curve on side that matched the radius of pulley (where the teeth are)

Eric
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Offline vintageandclassicrepairs

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Re: Hard to hold.....
« Reply #4 on: December 22, 2020, 02:55:19 PM »
Hi Ade
You would have it done on the mill in less time than it takes to set up in the lathe !!

John

Offline AdeV

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Re: Hard to hold.....
« Reply #5 on: December 22, 2020, 07:41:44 PM »
Thanks guys - this is exactly why I ask these questions, it never occurred to me to use bits of bar or square stock to fill the gaps! I like Eric's idea of machining the curve into them too, so you don't need to worry if it touches two or three teeth...

If I'm honest, though, the "do it on the mill" thought occurred when I was half way through posting the lathe question; I think I will do it on the mill - as John says, by the time I've sorted out 6 little blocks (I'm using a 6 jaw chuck!) & tappy-tap-tapped it all about the place to get it running dead nuts, I'd have finished it on the mill...

PS Phil - pretty sure this is a one-piece item, although I haven't looked particularly hard at it yet. Will give it a proper coat of looking at tomorrow.
Cheers!
Ade.
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Offline WeldingRod

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Re: Hard to hold.....
« Reply #6 on: December 22, 2020, 11:27:50 PM »
I agree that the mill is the way to go!

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Offline AdeV

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Re: Hard to hold.....
« Reply #7 on: December 23, 2020, 03:04:57 AM »
PS Phil - pretty sure this is a one-piece item, although I haven't looked particularly hard at it yet. Will give it a proper coat of looking at tomorrow.

I stand corrected - it does look like the flanges have been pressed on afterwards, there's definitely a join, and it looks like there's a tiny gap between the teeth and the edges.

However.... I don't fancy my chances of getting them off (or even one of them, which would be enough to hold the job in the lathe) without damaging it... so it's still a milling job I feel.
Cheers!
Ade.
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Or: Zhengzhou, China. An even longer way from anywhere...
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Offline Muzzerboy

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Re: Hard to hold.....
« Reply #8 on: December 23, 2020, 04:31:41 AM »
Sounds as if you need to get yourself 3 and 4 jaw chucks - what more excuse do you need!!

As it sounds as if you are not bothered about getting it dialled in deadly accurate, it would take no time at all to fling this in a chuck with 3 slugs of strip or bar and let rip. You don't even need 6 pieces with a 6 jaw chuck - 3 would do. Presumably you'd have to bugger about with clamps and packing to get the pulley set up on your mill. Six, two threes and half a dozen!

Offline RussellT

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Re: Hard to hold.....
« Reply #9 on: December 23, 2020, 05:43:41 AM »
Clamp it to a faceplate?

Russell
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Offline efrench

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Re: Hard to hold.....
« Reply #10 on: December 23, 2020, 09:49:29 PM »
I'd just 3d print a new one  :)

 
« Last Edit: December 23, 2020, 11:36:42 PM by Brass_Machine »

Offline vtsteam

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Re: Hard to hold.....
« Reply #11 on: December 23, 2020, 11:06:10 PM »
I love it when a Plan B comes together!
Steve
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Offline Brass_Machine

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Re: Hard to hold.....
« Reply #12 on: December 23, 2020, 11:37:10 PM »
You could even 3D print the spacers for between the jaws and pulley....
Science is fun.

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Offline AdeV

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Re: Hard to hold.....
« Reply #13 on: December 24, 2020, 04:19:31 AM »
Sounds as if you need to get yourself 3 and 4 jaw chucks - what more excuse do you need!!

Haha - I do have a 3-jaw and a 4-jaw. The 4-jaw is OK, but the 3-jaw is knackered... Next year, I'll buy a new Chinesium one, I think. I literally just got the 6 jaw fitted to the lathe a couple of weeks ago, I have no intention of removing it yet! Mainly because, on my lathe, changing chucks is (to quote lathes.co.uk) a "slow and tedious business". They're not wrong!

As it sounds as if you are not bothered about getting it dialled in deadly accurate, it would take no time at all to fling this in a chuck with 3 slugs of strip or bar and let rip. You don't even need 6 pieces with a 6 jaw chuck - 3 would do. Presumably you'd have to bugger about with clamps and packing to get the pulley set up on your mill. Six, two threes and half a dozen!

Indeed - "dead nuts" is not a requirement, the belt will simply be driving a mechanism that has to go round & round, it's not like it has to be super-mega-absolutely-accurate... That said...

You could even 3D print the spacers for between the jaws and pulley....

Dang it, why didn't I think of that!? I've even got 2 3D printers right here at the workshop....

However, as I've promised I'd do it today, and the "good" printer is already doing a long job that won't finish until late o'clock tonight.... futz it, I'm going with the mill option.


I'd just 3d print a new one  :)

An interesting proposal, but it'd take me longer to CAD it, than to machine the existing one. Of course, if I balls it up.... different matter!
Cheers!
Ade.
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Or: Zhengzhou, China. An even longer way from anywhere...
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Offline vtsteam

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Re: Hard to hold.....
« Reply #14 on: December 24, 2020, 04:45:18 PM »
Just one more side note. A faceplate doesn't have to be an "official" faceplate. It can just be a disk held in a chuck. Either indicate the face true, or face it true. Drill holes where needed for bolts or toe clamps as needed. Tap if helpful. Sacrificial after a bunch of uses. Handy to have around. Doesn't even have to be round if you have a 4-jaw.
I love it when a Plan B comes together!
Steve
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Offline awemawson

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Re: Hard to hold.....
« Reply #15 on: December 24, 2020, 05:23:16 PM »
Hey Steve, you could even superglue something down on one of those !!!!
Andrew Mawson
East Sussex

Offline vtsteam

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Re: Hard to hold.....
« Reply #16 on: December 25, 2020, 06:23:05 PM »
Yup, as long as the turned stock is thin and there's no major interrupted cuts -- superglue doesn't like levered side shocks.

But with SG on a plate like this you can definitely make thin washers this way (and precious few others). It's a variation on the older shellac on plate method of washer making.
I love it when a Plan B comes together!
Steve
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Offline PekkaNF

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Re: Hard to hold.....
« Reply #17 on: December 27, 2020, 04:47:56 AM »
Most often both all the pulleys dont't need to have both flanges. I had to to this sort of every now and then.

The flange comes off easily when little of that pressfit displacemet bulge on aluminium is turned off. I usually place thick enough roller bearing pins to proture above the guide flanges and chuck it there.  This does not offer enough grip to use twis drills, but has worked for boring (with a boring bar).

A littlecare is needed. Sometmes I turn a a split ring bushing to hold the pins more centered, sometimes I end better centering than the pulley had origininally. Looks like many fo the tooh belt balnk is pulltruded or extruded and then turned into pulleys.

If I needed to maintain the flanges, I probably would turn narow ring of aluminium to fit the ID and width between the flanges, OD to clear the langes and file the split area a bit of camfer to ease mounting it onto the pulley and chuck it into lathe.