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16th Jan 2020, 12:18 PM #1Golden Member
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Gear cutters - DIY Metric Conversion
I have an old Bandsaw that I’m looking to create a low range gearbox for as I want to convert it from wood to metal cutting. It’s a fun project and gives me an excuse to buy a dividing head for the mill.
I have a 1946 Hercus 9C too and whilst I’m in the making mood I’d like to add metric threading capability to it which requires making a 127/100 gear. So I’d like to confirm what cutters to buy in order to complete both projects.
I’ve seen references to 18DP 20 degree angle.
Is that correct? Is there a way I can measure the existing gears?
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16th Jan 2020, 01:13 PM #2Member: Blue and white apron brigade
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Sounds like a lot of work.
I'd be doing it with a couple of pulleys and maybe use the lathe to make custom pulleys if you can't find them commercially.
Some really cheap pulleys here
https://cononmotor.com.au/product-category/pulley/
They're only Al but they are well made and for what sounds like your intended use they should easily outlast your needs.
I found I could not even buy the materials for the price of these pulleys.
Of course if you are after "process" (the voyage) rather than "product" I can well appreciate that too.
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16th Jan 2020, 01:27 PM #3Golden Member
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Hey BobL, it’s a little bit of wanting to go through the process but also with my bandsaw reduction I have an issue.
I am trying to get a 48:1 ratio to get the blade down to steel cutting speeds.
In order to do that I need a really small lower pulley, so I was looking at 5M timing belts as I could use a small main pulley and not suffer belt slippage.
I was going to employ a jack shaft to manage that reduction (11T to 60T), however the largest internal bore on an 11T is 8mm and that shaft diameter seems way too small to not flex too much.
Also both the motors I have are 16mm/24mm main shafts, so I couldn’t even drive the smallest pulley directly off the motor.
Hence why I thought I could great a gearbox. As I could run quite a tight package and get to the desired speed using the 2 nested gears I have on my lathe. I was also thinking of a solution to swap between reduced speed and full speed so I could swap for Steel or Alu.
Plus I get to buy a dividing head
I’m open to ideas though if you think there’s a better way. My 2 concepts so far were:
A) 2 intermediate jack shafts but would require an ability to avoid 8mm internal bores but still get to 48:1 ratio. Ideally ability to change belts for full speed too.
B) gearbox like my hercus 9 with a lever to move from 48:1 to 1:1 (like the reverse lever maybe)
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16th Jan 2020, 02:18 PM #4Member: Blue and white apron brigade
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I'd buy the dividing head anyway - you'll find plenty of uses for it.
Below is a pic of a Milling Bandsaw blade (2" wide blade) roller gizmo I made a few years back, it was used to supposedly take cupping out of these wide blades.
https://metalworkforums.com/f65/t195...-2#post1893465
It uses a pair of 150 and 33 mm pulleys to generate a 20.6 reduction or from 1440 down to 70 RPM. Then I used VFD and ran the thing at around 30 rpm.
Using 220 mm pulleys would generate ~47:1 direct.
One way to use small diameter pulleys on larger (25 mm) shafts is to use a hub mount.
Machine the pulley onto the end the hub (made of larger stock) and bore the shaft size into the other end of the hub.
33 mm is less than desirable for many applications using standard belts but given how small the bandsaw is, it should be OK.
One of the forgiving thing about running at the low revs is that super rotary precision is not required - I found that our when making the blade flange/bearing for a thin kerf cutting saw that runs up to 13000 rpms.
BR1.jpg
BTW the gizmo is no longer required (it turns out I was running the BS sharpening wheel at a slightly non-perpendicular angle to the blade) so I am about to dismantle it.
The motor is from a Hercus Lathe and has been modified to 240V ∆ operation so it runs off a 240V VFD.
It's going to be installed back onto a Hercus that belongs to bloke from our mens shed.
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16th Jan 2020, 02:41 PM #5Golden Member
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Gear cutters - DIY Metric Conversion
I don’t need any encouragement to buy gear for the mill :O
Fantastic idea re the hub, hadn’t thought of that and it will fix my issues with the smaller pulley and will remove the need to do any gear cutting as this pulleys are cheap to buy off the shelf. I can also mount a larger pulley on the part of the hub on the motor too so I can change belts to support the 1:1 ratio.
Appreciate the input. Very helpful.
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16th Jan 2020, 03:53 PM #6Member: Blue and white apron brigade
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Here is another (extreme?) sort of example if what I called a hub type pulley.
The pulley on the RHS is the original one on the 1/2HP SP motor on my WW lathe. It had a 16 mm bore that went in just past the grub screw position..
I was replacing the 1/2HP motor with a 1HP 3P (plus VFD) motor with a 24 mm shaft.
The original pulley is not solid but hollow and for support has a (cast) sleeve about 25 mm in diam but if I bored it out to 24 there would no metal left.
So I made a replacement pulley out of solid Al rod and fortunately there was also enough space to locate the grub screw away from the pulleys .
The VFD works so well I rarely swap belt positions and could have got away with just say the 2nd and 4th pulley position.
IMG_3367.jpg
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16th Jan 2020, 05:58 PM #7Gear expert in training
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Just FYI, large prime numbers do not play nicely with dividing heads. You'll either need a 127 index plate for a normal dividing head or a universal dividing head that has a gear train setup for differential indexing and those are not cheap.
I might be able to hob one for you at work, I'll check tomorrow.
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16th Jan 2020, 08:37 PM #8Golden Member
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A 47/37 pair will give you a ratio of 1.270270 and that's a lot less teeth to cut for a tiny difference in ratio. There are calculators online like this one that will print out prime number templates i.e. the 37 and 47 teeth.
https://www.cgtk.co.uk/metalwork/calculators/divider
Bill
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16th Jan 2020, 08:41 PM #9Golden Member
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With some extra info I have some other ideas on how to approach this.
Will update the bandsaw thread I have running.
Bills thoughts have me working some ideas using timings belts and I have a thought on how I can make a quick change gearbox too. Watch this (or the other to be more specific) space.
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16th Jan 2020, 09:59 PM #10Member
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A 80/63 compound is an even closer ratio (actually the closest before getting up to 127 teeth)
This can also make use of an existing 80 tooth gear
But note that a 63 tooth can be cut on a 90:1 dividing head but not on a 40:1
If you can cut 63, it is a very simple option
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16th Jan 2020, 10:12 PM #11Philomath in training
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Probably half correct. 18DP is likely but I suspect that the pressure angle is 14 1/2 degrees, just because of the age of the machine. If you roll a gear along a line of bluetak or plasticene you may be able to get a good enough impression of the teeth as a rack that you could measure the angle of the teeth.
To do that in one step you would normally use a wormgear and worm - you would have to cut a 48t wormgear, but that can be indexed with semi-universal dividing head.
One of those was made up a few years ago. Not sure where it ended up. Perhaps with Ewan? (Ueee) Haven't seen him here for a while but he is in Canberra, so if he has it, it might be worth the drive.
Michael
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16th Jan 2020, 10:13 PM #12Golden Member
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Wealth of knowledge on here. Appreciate all the tips.
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17th Jan 2020, 07:26 AM #13Philomath in training
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Another one of those thoughts that occur when you are trying to get to sleep...
Cutting speed for MS is around 30m/min. Cutting speed for Al is around 90m/min. A wood cutting saw (circular or band) can be used for cutting Al which suggests that a cutting speed for wood is also around that speed. The exact number is in the TBD column but does not matter. The point is that that is only around a 3:1 ratio. Even if that were pushed to 4:1 or 5:1, that is still a long way from 48:1.
(I note that reading Wikapedia they quote MS speeds from 3 to 38 m/min. An order of magnitude spread is not really very helpful. However, the numbers they give are referenced as being taken from a book on auto screw machines - those things run in completely different ways to a manual lathe, so I would suggest that the figures they quote should only be considered valid in relative terms)
Michael
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17th Jan 2020, 07:39 AM #14Golden Member
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Gear cutters - DIY Metric Conversion
Michael; I have the details for the bandsaw cutting speeds in SFPM. From what I’ve read I’m aiming for:
1000 SFPM (wood/Alu)
100 SFPM (steel)
50 SFPM (Stainless)
I very rarely cut SS (if ever) so I’ve been aiming for 100 and 1000
Using this site I’ve been able to work out that my motor (1440 RPM) and 14” wheels would need a 4:1 and 40:1 ratio for these.
My plan was to use a combination of timing pulleys to come up with both:
2 x 2:1 (Alu)
6:1 and 8:1 (steel)
My plan is to try and put both pulleys on the motor and also the bandsaw. The inner pulleys will be put on a central jack shaft with plain bronze bearings to allow them to spin freely. I am going to attempt a dog clutch setup for both inner pulleys so I can use a selector to move both dog clutches at the same time.
It might not work but I’m hoping if I can make it simple and sturdy enough I can get it to work.
I will also have a VFD for additional adjustment.
It’ll be a fun exercise anyway on the lathe and mill.
To show how serious I am, I’ve bought a moleskin notebook and mechanical pencil to draw up my mad ideas on the train...
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17th Jan 2020, 08:20 AM #15Most Valued Member
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FWIW, my vertical BS has a 7:1 primary reduction, a 6:1 final reduction and a 5speed stepped pulley arrangement in between those drives that ranges from about 1:2 - 2:1.
It's 12" drive wheels and 1440 rpm motor.
It's in the ball park of what you are aiming for.
Steve
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