Help Needed: Eriksen Lathe Thread Cutting

[BaronJ]

Test gears 3D printed. Will mount on the weekend and see if they fit correctly....

Attachment 389431

Nice !

[racingtadpole]

So... 14 pages in.. I have to ask..

Would you like to borrow an M20 Die?

[Jekyll and Hyde]

Test gears 3D printed. Will mount on the weekend and see if they fit correctly....

Attachment 389431

Looks like the front fell off. And the sides. That's not typical. Might make for an interesting test cut.

I'd suggest you might be able to get it to fit on the bed by splitting it in half and opening up the bore, then redesign the gear it compounds with to have a boss and bolt the two halves of the 127 to that gear?

Just be nice to confirm 100% with at least a scratch pass that the gearing will definitely give what you want, before you take that shiny m=1.75 cutter out of it's little plastic bag and start murdering metal for hours. What, you thought I'd miss that little Easter egg in there?

[Mk1_Oz]

So... 14 pages in.. I have to ask..

Would you like to borrow an M20 Die?

Baahaaaaaa. But then I would not have learned a heap, been likened to a moose and had several great forum members thinking!

Jacket & Hide - yeah I hoped nobody would notice . To print a whole gear would have meant printing quarters and I was not confident that they would glue up in perfect alignment due to shrinkage etc. I am happy just to ensure the gears physically fit and have sufficient adjustment to get the correct backlash.

[Jekyll and Hyde]

Baahaaaaaa. But then I would not have learned a heap, been likened to a moose and had several great forum members thinking!

Jacket & Hide - yeah I hoped nobody would notice . To print a whole gear would have meant printing quarters and I was not confident that they would glue up in perfect alignment due to shrinkage etc. I am happy just to ensure the gears physically fit and have sufficient adjustment to get the correct backlash.

How rude. Now everyone is going to watch me all the time, how am I going to get away with it now.

I don't think they need to be in perfect alignment, even if there's four joins that aren't quite right, as long as they're good enough to keep driving the next gear in the train you'll get a decent enough result for a quick test - just maybe with a tiny cyclical imperfection every x percent of thread.

But up to you, I just hope that my confidence in my own maths is indeed correct if you jump straight to making the metal ones after this - I'd hate for you to spend hours making a set of gears that don't work!

[Mk1_Oz]

just saw that auto correct renamed you Jacket & Hide....

[Michael G]

Is that an involute profile you've modelled up on those gears? (doesn't look quite right)

Michael

[Mk1_Oz]

Is that an involute profile you've modelled up on those gears? (doesn't look quite right)

Michael

Certainly is

[Mk1_Oz]

3D printed gears fitted - all good. I realised I could not take a test cut with these as I did not model the spline on the gearbox input shaft.

20201107_132745.jpg20201107_132736.jpg


Fitting the idler will be difficult as the gear partly covers the slot that a mounting bolt would go in. I will have the mount the gear support arm using a countersunk nut.

Ordered the wrong cutters so waiting for the correct ones to arrive.

I have ordered some ductile iron to cut the gears from and some LG2 bronze for a bushing. Anybody think this is the wrong material??

[Michael G]

Normal cast iron probably would have been fine. Most of the change gears I make are from steel; for low power applications it won't really matter. Simon's bandsaw is still going fine with a delrin gear.

Michael

[Mk1_Oz]

Getting closer to cutting the gears. I have started to make the 127 hole plate and have the ductile iron blanks cut to size.

I have been reading through the Machinery's Manual and some online resources and believe that the depth of cut of a module tooth is 2.25 x MOD (where MOD> 1.25). I therefore need to cut all my 1.75 MOD teeth to a depth of 1.75 x 2.25 = 3.9375mm?????

As elanjacobs suggested I have taken 0.3mm off the OD of the blanks so the actual measured depth of cut should be 3.9375 - (0.3/2) = 3.7875mm?????

Am I correct here? Keith Rucker developed some elabourate spreadsheet to calculate his DP gear cutting but I am not seeing that it is all that complicated. Would hate to destroy my blanks!!!!!!!

[pipeclay]

Yes that would be correct, my first reply related to 14.5 PA ( 2.157 x mod ) not 20 PA.
Are you using a 40/1 or 90/1 indexing ?

[elanjacobs]

Yes that would be correct, my first reply related to 14.5 PA ( 2.157 x mod ) not 20 PA.

The full tooth depth is always 2.25 x Mod, regardless of pressure angle, for a true involute gear.

The 2.157 number is for the "composite" system, which is an involute curve around the pitch line, but modified with cycloidal curves to eliminate interference in gears with low numbers of teeth.

[Mk1_Oz]

Yes that would be correct, my first reply related to 14.5 PA ( 2.157 x mod ) not 20 PA.
Are you using a 40/1 or 90/1 indexing ?

cheers.

40:1

[Mk1_Oz]

OK I need some more help........

I have just had my 2nd go at putting the holes in my 127 hole plate. The first time I used a 2nd hand and unknown 3mm slot mill that made oversize holes then snapped on the 9th hole. I then bought a couple of carbide 3mm slot drills from General Tools. The first snapped as soon as it touched the ductile iron surface and the second snapped off in hole number 2.

I have the slot drill turning pretty fast although I do not actually know how fast. The first new one snapped I believe as I had the speed too low and was using the quill handle to 'drill' which probably gave too much downfeed. The 2nd slot mill I ran much faster and used the knee to 'drill' much slower.

Any hints why these all snapped? Speed? Feed? Material? Cheap slot mill?

I will now get a 3mm R8 collet and use a drill bit instead. I wanted to only drill halfway through the plate so that I could use the other side for other hole patterns if I ever need to but I'm over it and will just drill right through.