Myford change gears on a Harrison L5?

[smashweld]

my L5 only came with 3 gears, a 50t, 60t and a 70t...

the prices for 'genuine' Harrison gears are mad, especially buying them individually! Myford gears are far cheaper and easier to find so was thinking I could buy Myford gears, bore them out and increase/cut new keyway

from what I can see the Myford gears are 20DP, 5/8" BORE WITH A 1/8" KEYWAY, Harrison L5 gears are 14DP, 7/8" bore, 1/4" keyway, the Myford gears are also thinner



assuming I forget about the gears that came with it and just use all Myford gears does that seem like a reasonable solution?

 

[Pete.]

Yes it does, but you might find some of the gear trains as set out in the chart unachievable without idlers or factoring-up the tooth counts.

Does your lathe have only change gears for feeds and speeds or does it have a gearbox and a small selection of gears to compliment?

 

[smashweld]

it has the 3 speed gearbox and the 50, 60 and 70 gears that were attached to it when bought

the only standard thread I can get with that is 7tpi, or there's one really close to 3.5mm pitch, the slowest speed for the power feed is also too fast with those gears/box

 

[Rrobson]

What about new ones from someone like hpc gears? They do imperial gears.
That or fit a full set of equivalent metric gears. Doesn’t really matter what you fit as long as they have the correct number of teeth.
The issue with fitting smaller gears is they are more likely to become damaged if you take heavier cuts, obviously a larger Harrison will allow far heavier cuts than a myford, so they’ll have to transmit more torque possibly ending up in failure if under spec’d

 

[Seadog]

One of the members of the Boxford group has developed a very elaborate programme for calculating ratios of any setup, which also shows the percentage errors with each configuration.

Ride The Gear Train free software by Evan Lewis

 

[Pete.]

I can't see it being a problem my Monarch and the CVA use 32DP gears for the metric set.

 

[dieselsamurai]

Ive been running my lathe with 3d printer change gears for a year now no breakages...

or this guy does gears to spec at good prices

you_engraving on eBay

Follow you_engraving on eBay. Buying, Selling, Collecting on eBay has never been more exciting!

www.ebay.co.uk

 

[smashweld]

One of the members of the Boxford group has developed a very elaborate programme for calculating ratios of any setup, which also shows the percentage errors with each configuration.

Ride The Gear Train free software by Evan Lewis

I was thinking of doing something in Excel but that is elaborate as you say!...did this spreadsheet for the 3 gears and gearbox I have just now...

Driver	Driven	Gearbox	TPI	pitch in mm
50​	60​	1​	4.8​	5.291667​
50​	60​	2​	9.6​	2.645833​
50​	60​	1.5​	7.2​	3.527778​
50​	70​	1​	5.6​	4.535714​
50​	70​	2​	11.2​	2.267857​
50​	70​	1.5​	8.4​	3.02381​
60​	50​	1​	3.333333​	7.62​
60​	50​	2​	6.666667​	3.81​
60​	50​	1.5​	5​	5.08​
60​	70​	1​	4.666667​	5.442857​
60​	70​	2​	9.333333​	2.721429​
60​	70​	1.5​	7​	3.628571​
70​	50​	1​	2.857143​	8.89​
70​	50​	2​	5.714286​	4.445​
70​	50​	1.5​	4.285714​	5.926667​
70​	60​	1​	3.428571​	7.408333​
70​	60​	2​	6.857143​	3.704167​
70​	60​	1.5​	5.142857​	4.938889​

 

[RichardM]

I think @Johnnybravo had some gears for sale a bit ago, they may be more suitable for conversion if he still has them. Can't remember the details of them though.

 

[Johnnybravo]

I think @Johnnybravo had some gears for sale a bit ago, they may be more suitable for conversion if he still has them. Can't remember the details of them though.

Scrapped

 

[Agroshield]

What about new ones from someone like HPC gears? They do imperial gears.

14DP is a bit of an oddity and is not really made by anyone any more. Standard imperial gears go straight from 12 to 16.

Boston Gear in the US used to list 14DP but that will not be cheap.

---

The closest metric equivalent, which would mean replacing everything, is 1.75 MOD. They are no so far off 14DP that the existing charts might work.

It would be possible to experiment. Make up a load of plywood disks*, each of the pitch diameter of the equivalent 1.75 MOD gear. See if the physical limits of the machine will accommodate them without problem.

It would also be easy to make plywood disks to 20 DP specification to see what problems might arise.

I think that 14/20 is 7/10, so a 20DP gear would be 70% of the diameter of the same tooth count 14DP gear. That means to preserve the ratio and the centre distance, the tooth count of a meshing pair would have increase by 10/7, which is not a nice number (change gears usually go up in fours or fives, not sevens). It is not like going from 10 DP to 20 DP where you just double the tooth count and everything works out.

*or thick cardboard if you have a laser cutter or Cricut. These days the plywood blanks might be more expensive than the cast iron gears.

 

[smashweld]

Gear Dimensions Calculator | Evolvent Design

Calculator to make the right dimensions for a gear or gear blank: calculate gear pitch, outer diameter (OD), root diameter, and clearance.

evolventdesign.com

I found this gear size calculator...Didn't realise 20dp would be so much smaller, one problem is the 20t gear, there's basically going to be nothing left apart from the teeth when bored out to 7/8...

Inputs
Number of Teeth: 20
Diametral Pitch: 20
Pressure Angle: 14.5 degrees
Gear Type: External

Outputs
OD Reference: 27.9400 mm 1.1000 in
Pitch Diameter: 25.4000 mm 1.0000 in
Root Diameter: 22.2250 mm 0.8750 in


don't think there should be many problems other than that tho, just need to use a big gear for the idler...going to take some measurements between gears/banjo movement and mock it up in sketchup

 

[Pete.]

Gear Dimensions Calculator | Evolvent Design

Calculator to make the right dimensions for a gear or gear blank: calculate gear pitch, outer diameter (OD), root diameter, and clearance.

evolventdesign.com

I found this gear size calculator...Didn't realise 20dp would be so much smaller, one problem is the 20t gear, there's basically going to be nothing left apart from the teeth when bored out to 7/8...

Inputs
Number of Teeth: 20
Diametral Pitch: 20
Pressure Angle: 14.5 degrees
Gear Type: External

Outputs
OD Reference: 27.9400 mm 1.1000 in
Pitch Diameter: 25.4000 mm 1.0000 in
Root Diameter: 22.2250 mm 0.8750 in


don't think there should be many problems other than that tho, just need to use a big gear for the idler...going to take some measurements between gears/banjo movement and mock it up in sketchup

You can't bore a 20dP out to 7/8" bore the hole will break into the base circle, or if it doesn't then the keysway certainly will.

 

[smashweld]

Ahh.. does that go for all sizes?
I only noticed that the 20t would be impossible

 

[Pete.]

No, other sizes will be OK so long as the bore isn't too close to the base circle. Of course, if you use myford gears you don't need to use the harrison gear posts you could make myford sized ones and it would be less trouble than modifying all of the gears too.

 

[smashweld]

I did think about that...the bottom one I had out when I had the gearbox apart to clean out all the grease, the middle just comes off...I never tried to remove the top one though, read not to disturb the headstock, no doubt it's fine if you know what pins etc need to come out

but you're right it would be less hassle and solve the problem of the 20t

 

[Rrobson]

14DP is a bit of an oddity and is not really made by anyone any more. Standard imperial gears go straight from 12 to 16.

Boston Gear in the US used to list 14DP but that will not be cheap.

https://www.hpcgears.com/pdf_c33/23.126-23.131.pdf

Although it states 20 degree pressure angle, I’ve no doubt for a lathe it’ll be fine. And if you bought half a dozen it wouldn’t matter if they’re being used together

 

[Agroshield]

...going to take some measurements between gears/banjo movement and mock it up in sketchup

Once you have the machine modelled, copy the geometry and scale it down to 70% (so it is correct for the 20DP gears). Then centre the copy on the spindle and see where the leadscrew input (and banjo centre of rotation) would be. See if you can fix a gear and banjo* in that location. Then from the back of the gear that would be the input to the leadscrew put a timing pulley with 1:1 toothed belt drive to the real leadscrew.

It might be easier to do it in the opposite direction - centre the geartrain on the leadscrew input and have the belt drive from spindle to input gear. That would eliminate the problem with not being able to bore the input gear out enough. The timing pullies could be any size to fit the spindle, so long as they are both the same size. It is not so often that you need a small gear on the end of the leadscrew so the bore limitation will be bypassed.

* a Myford banjo from a breakers might then work to save making one.

 

[smashweld]

I don't think the Harrison L5 really has a 'metric set' btw, just adding a 127t gear allows for all metric pitches (from M6 up anyway)....the 95t and 120t are the only 'special' gears outwith the standard set

https://www.picclickimg.com/images/g/AFcAAOSwuGxiBidI/s-l1600.jpg

https://www.model-engineer.co.uk/sites/7/images/member_albums/93892/898857.jpg

 

[Tinbasherdan]

What tooth count gears do you need? I’ve a stash of 14dp gears I got given ages ago, they’ll just need boring to suit