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Tips on machining pulley grooves

 

I was not as sophisticated as any of this.? I took a 1/4" pointed nose carbide tool and cut a groove that works well enough with an O-ring.
 

On Sun, Sep 17, 2023 at 12:40 AM, Mike Gidley wrote:
This what i was thinking Peter
I made a tool like this for undercutting a ring I was machining off an 8" diameter bit of aluminium - obviously it was all much bigger than a Unimat. I also cut some Vee groove pulleys on a big machine, by cutting to the bottom of the groove with a modified parting tool - a grooving tool - to take out most of the material. You could make a small tool like this from something like O1 carbon steel by drilling a recess and filing back to the round profile. You probably don't need to harden the steel for a small number of cuts like this, but you could. If you had made the pulley from brass it would have been easier, and different grades of Ali can be very different in there machinability. Best is 2011, which is leaded, and definitely cuts much more readily than many other grades. Also consider various plastics - Acetal (Delrin) cuts very nicely. Another approach would be to cut the groove with a ball nose milling cutter held in something like a Dremel in the tool post. Not sure how large a cutter you can put in a Dremel, but something like that. An old way to do it would be to put the cutter in the lathe chuck and rotate the pulley horizontally against it on the cross slide with some sort of gearing arrangement. Various possibilities if it really won't work by the direct turning approach.
 

The traditional acronym is PEBCAK: Problem Exists Between Chair and
Keyboard.


On 9/17/23 12:22 PM, Peter Brooks wrote:
On reflection, I think it was ¡®the nut between the chair and keyboard¡¯,
which makes much more sense and is closer to your definition :-)
_._,_._,_
--
Elliot Nesterman
elliot@...
www.ajoure.net

"The finest jewel cannot disguise a flawed character."
 

All of my Unimats run a round section belt in a V ???¡á?
 

That's right.? My mistake.? I got mixed up (I sold my Unimat about a year ago and don't have it to look at anymore).? I think I conflated that with another small lathe I once had that DID have round grooves for round belts.

In that case, I certainly agree that a center plunge cut (or cuts) followed by angled cuts is the way to do it.? (Well, "a" way but the way I would do it.)? No forming tool approach.

Charles E. "Chuck" Kinzer

On Monday, September 18, 2023 at 12:13:17 AM PDT, Unimat Matt <matthewtay2020@...> wrote:


All of my Unimats run a round section belt in a V ???¡á?

 

Whaaaat? (throws hands into air, runs to check¡­)

Phew, my U3 definitely has round section pulleys.

I realise now that round section belts run perfectly well in V grooved pulleys, which would have been considerably easier¡­ I think I must be developing some engineer¡¯s OCD (is this a good thing? I don¡¯t know¡­)

Anyway, the first pulley (the motor one) is done, thankfully without burning out the old motor.


(I knew that test spindle that I turned a while back would come in useful one day).

The old belt just?stretches, so I can use the new motor(s) to turn the next pulley, which will then be installed and used to turn the last one.


When finished it will be 1:1 gearing, as I have the PWM controller for speed.

Cutting waste out with a parting tool certainly helped, but I think this is at the limits of the U3, if not slightly beyond it. Very slow progress!
 

Keith, I did have another idea¡­ What I¡¯m trying to do is essentially cut an internal semi-circular (ball) shape but there is obviously no room to swing a cutter on a pivot at the edges (it would be on a ridiculously small scale anyway).

I wondered if a cutter held vertically with a simple lever to rotate it would work. Something like a cut-down, ground-down and re-shaped small boring bar (3/16 shank)?

The cutting surface would be greatly reduced, as would load on the drive train. A ¡®proper¡¯ cutter shape could be used to suit the material Arranging it could be quite simple, dropped through a block of half inch square stuff bolted into the top of the tool holder. Disc type stop with a grub screw against a flat. The issue I think would be killing excess wobble (and therefore chatter) while still allowing it to be rotated.

Feasible?
 

Building the new pulley out of 2 or 3 pieces seems like it might be a good approach.
?
-Guy-

On 09/16/2023 5:32 PM EDT Julius Henry Marx <sawbona@...> wrote:
?
?
On Sat, Sep 16, 2023 at 06:20 PM, Peter Brooks wrote:

... the U3 probably isn¡¯t quite up to the task.
There's a more than one way to skin a cat, just that sometimes you have to push the envelope a bit more than would otherwise be comfortable.
I was in the exact same spot, did not want to spend absurd money on something I was (reasonably) sure I could make myself but only had my Unimat 3 to work with.

Check thread at ME.

Best,

JHM

 

Another option if you can't shape a cutter.? ?Go to a chain saw shop or dealer and purchase a chain file, they come in various diameters, 3/32 or 1/4" would be good, put them on the tool holder or hand hold them you should be able to get a good finish fast.? ?Their teeth are on a diamond pattern as they are used to cut at an angle for sharpening chains.? ?Just my option.? ?Harbor Freight also has diamond burrs? for dremel tools with 1/8'' shanks that might work also.?

pat
 

You could try something completely different.? I actually did this myself on my old south bend lathe.
You could mount a router or dremel type tool and put a ball type cutter in it and plunge while rotating the head stock slowly or by hand.
Then you can sharpen a form cutter razor sharp and do your final .005 or .010".

You can probably do 0.010 - 0.020 depth of cuts on solid stock or plunge with a cutoff tool then mill with the router then finish with the form tool.

I created an 8" dia aluminum drum approx 12 inches long with a 0.25" pitch cable groove by engaging the threading (a bit jury rigged) on that lathe.
My U3 I am sure I could employ similar methods for straight grooves.


On Sat, Sep 16, 2023 at 4:12?PM Peter Brooks <peter@...> wrote:

As part of my 24v re-motoring exercise I¡¯m making new pulleys from aluminium. I¡¯m not finding it easy to machine the groove for the belt and would appreciate any tips (apart from ¡®buy them online¡¯ and ¡®do it on a bigger lathe¡¯ - I just have the U3).

I use ¡®O¡¯ rings for belts, they have a 5mm cross-section diameter. The finished inner diameter at the bottom of the groove will be 38mm. The pulley body is 9mm thick to allow for the flange portions either side of the groove.

For a cutter I first tried a 6mm drill bit cut off at 45 degrees and then milled clean. Blimey a drill bit is hard to saw with a hacksaw. Two blades later¡­ the endmill had no problem however.? The finished ¡®cutter¡¯ didn¡¯t cut very well though.

Next I ground a cutter (my first!) from a 6mm blank. Semi-circular, with a 6 degree angle, and some top relief (as recommended for aluminium I believe). This was moderately successful but it is doing more of a scrape than a cut. It is literally ¡®stop start¡¯. It did however produce some beautiful swarf, almost like snowflakes, or frost.




It is making pulleys - but painfully slowly. I have more material to remove and it is not working well at the moment.

I think I should be taking out excess material in smaller chunks first then finishing with the shaped tool, but a plan to do this is puzzling me given the finished shape. It¡¯s taken a long time to get this far from a large chunk of aluminium and I don¡¯t want to ruin anything!


So far I¡¯m going in at one position. I did wonder if alternating cuts between two slightly altered positions (kind of left and right) would be beneficial - the cutter would (or might) only be using 50% of the cutting edge.


I¡¯m making three pulleys in all - one for the motor and one each for the lathe and mill.

As usual I have very little idea what I¡¯m doing so am looking to tap into folks wealth of knowledge and experience. Any tips gratefully received. Thanks!

(Sorry for the overlong post - the quick version would be ¡®How would you make a pulley groove?¡¯ :-)
 

when i needed pulley grooves on the motor i now use on my unimat 3 it was a simple as firing up the motor and attacking the gear on the end of the shaft with a round file until it was deep enough for the? belt.


------ Original Message ------
From "Tool247" <Sjkochan@...>
Date 20/09/2023 13:13:40
Subject Re: [Unimat] Tips on machining pulley grooves

You could try something completely different.? I actually did this myself on my old south bend lathe.
You could mount a router or dremel type tool and put a ball type cutter in it and plunge while rotating the head stock slowly or by hand.
Then you can sharpen a form cutter razor sharp and do your final .005 or .010".

You can probably do 0.010 - 0.020 depth of cuts on solid stock or plunge with a cutoff tool then mill with the router then finish with the form tool.

I created an 8" dia aluminum drum approx 12 inches long with a 0.25" pitch cable groove by engaging the threading (a bit jury rigged) on that lathe.
My U3 I am sure I could employ similar methods for straight grooves.

On Sat, Sep 16, 2023 at 4:12?PM Peter Brooks <peter@...> wrote:

As part of my 24v re-motoring exercise I¡¯m making new pulleys from aluminium. I¡¯m not finding it easy to machine the groove for the belt and would appreciate any tips (apart from ¡®buy them online¡¯ and ¡®do it on a bigger lathe¡¯ - I just have the U3).

I use ¡®O¡¯ rings for belts, they have a 5mm cross-section diameter. The finished inner diameter at the bottom of the groove will be 38mm. The pulley body is 9mm thick to allow for the flange portions either side of the groove.

For a cutter I first tried a 6mm drill bit cut off at 45 degrees and then milled clean. Blimey a drill bit is hard to saw with a hacksaw. Two blades later¡­ the endmill had no problem however.? The finished ¡®cutter¡¯ didn¡¯t cut very well though.

Next I ground a cutter (my first!) from a 6mm blank. Semi-circular, with a 6 degree angle, and some top relief (as recommended for aluminium I believe). This was moderately successful but it is doing more of a scrape than a cut. It is literally ¡®stop start¡¯. It did however produce some beautiful swarf, almost like snowflakes, or frost.




It is making pulleys - but painfully slowly. I have more material to remove and it is not working well at the moment.

I think I should be taking out excess material in smaller chunks first then finishing with the shaped tool, but a plan to do this is puzzling me given the finished shape. It¡¯s taken a long time to get this far from a large chunk of aluminium and I don¡¯t want to ruin anything!


So far I¡¯m going in at one position. I did wonder if alternating cuts between two slightly altered positions (kind of left and right) would be beneficial - the cutter would (or might) only be using 50% of the cutting edge.


I¡¯m making three pulleys in all - one for the motor and one each for the lathe and mill.

As usual I have very little idea what I¡¯m doing so am looking to tap into folks wealth of knowledge and experience. Any tips gratefully received. Thanks!

(Sorry for the overlong post - the quick version would be ¡®How would you make a pulley groove?¡¯ :-)
 

Yes, the 3 has round grooves, the DB / SL / SL1000 V-grooves.

On Monday, September 18, 2023 at 02:24:42 PM EDT, Peter Brooks <peter@...> wrote:


Whaaaat? (throws hands into air, runs to check¡­)

Phew, my U3 definitely has round section pulleys.
 

On Sat, Sep 16, 2023 at 09:22 PM, Bill in OKC too wrote:
...perhaps used a hacksaw blade, or piece of hacksaw blade, as a parting tool before cutting to depth with your profile cutter.
This was a great tip. The piece of hacksaw blade was only about half the thickness of the parting tool I was trying to use. With the motor out of the way I was able to get an indicator on the back of the slide. In, out, back and forth guided by the indicators in order to give side clearance to go deeper in with the hacksaw blade.

It was easier to rough out but still left pronounced (if small) steps, and the profile cutter had considerable work finishing it off.



Anyway, that was the third pulley (for the milling attachment) finished. Or so I thought...

Zounds!? *#^%!!!? And other expletives. The pulley thread on the U3 milling attachment is M12 x 1 !!!? Yes, the spindle thread is the standard M14 x 1, so I just assumed...

So faced with making pulley number 4 (sigh), and the increasing realisation that it is the size of the cutting surface that is the issue I thought it would be worth testing out my other idea:

I wondered if a cutter held vertically with a simple lever to rotate it would work. Something like a cut-down, ground-down and re-shaped small boring bar (3/16 shank)?
A piece of 10mm square bar attached to the top of the tool holder, a re-ground 6mm drill bit dropped through a hole in the bar, and an aluminium disc to rotate the cutter by hand. I tried to grind to the proper angles and relief for aluminium, and it worked a treat. Because the cutting surface is very small (tiny even) it never felt overloaded or unsafe, and the motor speed didn't dip at all!? In fact the cut was very 'sweet', with great feel feedback through the disc. Rotation and progress was obviously slow (one division, 0.05mm at a time, two passes each time) but the profile was always going to be absolutely correct.? You can remove the cutter / disc assembly any time to re-sharpen, and just drop it in again. I'd recommend it as the least stressful way to cut pulleys on the U3. (The first photo below shows a non-cutting position, you can see my sketchy pencil arrow on top of the disc to show where the cutting edge is).





Thanks everyone for your replies and suggestions!? I've learnt an awful lot through the re-motoring process, and the U3 with it's DC motor is better than ever.
 

I have made several pulleys for the round belts and they don¡¯t seem to care what the groove shape is. They are ¡®grabby¡¯ enough that they just work.?
Hint, don¡¯t use a Deutz diesel engine piston for stock to make pulleys. The most gummy stuff I¡¯ve ever cut. Had to do it in my big lathe and it was a chore. I made this contraption experimenting with motors and stuff.?

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