Author Topic: Revisiting the buttress thread. (Read 14884 times)

NeoTech · « **on:** April 09, 2013, 01:43:31 AM »

So i my uncle pointed out to me that a 1.666 thread in mm equals to 1 and 2/3 mm. And converted to turns that would be 5/3 turns as a ratio.

When i threaded the buttress i made a hilarious amounts of calculations to arrive at the correct gearing.

How would you convert a turn ratio like 5/3 to a gearing setup. It would most likely be more precise than what i arrived at.

// Andreas

chipenter · « **Reply #1 on:** April 09, 2013, 02:44:21 AM »

Multiply both numbers by the same amount ie 5\3 X 10= 50 \30 until you have numbers that match your change gears .

NeoTech · « **Reply #2 on:** April 09, 2013, 02:30:31 PM »

In another thread i calculated the pitch of 1.666666 as a rounded fraction to 1.667 (i was shown). By setting my lathe gearing to a 3mm pitch i then did 3 / 1.667 = 1.8 and then went (1/1.8 * 10) * 3. Wich ended up as a 30/120/54 gearing on my lathe.. that worked.. nothing about that.. BUT.. if i do the math as ratios i end up with a 30/120/50 gearing instead.. will this be more or less accurate than my initial calculations?

Why im asking cause my ER32 collet i made threads into the drawbars but dont seat really well.. i think it has something todo with fraction "off" in the threading.

vtsteam · « **Reply #3 on:** April 09, 2013, 09:19:06 PM »

would it be 40/120/24?
or 35/105/21
or 30/90/18
or 25/75/15

vtsteam · « **Reply #4 on:** April 09, 2013, 09:47:37 PM »

45/135/27
50/150/30

5x/15x/3x?

vtsteam · « **Reply #5 on:** April 09, 2013, 10:01:23 PM »

Neotech -- apologies for the above if I don't understand the question -- are you essentially trying to get a step up ratio of 1.6666666.... with a train of 3 gears (or ratios)?

NeoTech · « **Reply #6 on:** April 09, 2013, 11:42:32 PM »

Vtsteam you are correct i try to get the accurate gearing for the 1.666 butress thread used on my aciera mill.

RussellT · « **Reply #7 on:** April 10, 2013, 05:25:57 AM »

Hi Andreas

I've read this a couple of times to get my head around what you're trying to do.

As I understand it your lathe has a gearbox but 1.66667 mm is not one of the pitches provided so you're doing it with changewheels as well.

You've set your gearbox to 3mm and your gears to 30/120/54.

If I understand this correctly - the middle gear can be any size you like as it is an idler - it only needs to be there because the other two gears won't touch each other. 30 and 54 give the correct ratio to convert 3 to 1.666667 (3*30/54 = 1.6666667).

This should work OK as long as the normal gear setup for using the gearbox is a 1:1 ratio (ignoring the middle gear).

If you used 30/120/50 you would get 3*30/50 = 1.8

Russell

NeoTech · « **Reply #8 on:** April 10, 2013, 05:55:46 AM »

Ah well i think i was fuzzy with my goals here.. I made the 30/120/54 gear change and threaded a ER32 collet that way.. Yes it works, but its a sloppy thread. Its accurate enought to take thread and putting force on it works..

But... (isnt there always a but).. when putting the same collet in the horizontal feed with different drawbar the slop becomes more apparent.. And i thought to myself.. well i could prob. redo this. But should i recalculate the thread to come closer to the ratio that was originally used. That 5/3 ratio.

But you kinda pointed out that my math was way off there.. =)
Converting the thread to a ratio by doing some excessive simplification doesnt really work out.. the 1.666mm thread, that can be read as a 1 and 2/3 of a milimeter, is a 5/3 ratio. But cant be calculated as i tried to.

And now when this is cleared up i need to revisit this damn buttress in a other fashion i guess to get the thread tighter and well better. =)
I do must say i get a better and better understanding of how to cut and calculate .. annoying thread pitches. ;)

RussellT · « **Reply #9 on:** April 10, 2013, 07:16:11 AM »

If you prefer to look at it another way you are trying to cut a thread with a pitch of 5/3mm which is your 5:3 ratio.

Your gearbox is set to 3mm so you need to add in a 1:3 ratio as you are measuring in single millimetres.

That gives 5:3 *1:3 = 5:9. Multiply by 6 and you have 30:54.

If you set your gearbox to 1mm the calculation would be simplified. You would need 5 turns of the gearbox gear for 3 turns of the spindle gear. 5:3 *10 =50:30. Note that it's 50 on the spindle and 30 on the gearbox as if the gearbox is set to 1mm it has to turn faster than the spindle.

Russell

NeoTech · « **Reply #10 on:** April 10, 2013, 07:22:26 AM »

Aahhh there was the missing piece of information.. howto take the ratio in the box into account.. sweet.. ok. well then im spot on i guess.. =)

Need to make me a grinding rest for toolbits and get back to get the right somehow. =)

Anzaniste · « **Reply #11 on:** April 11, 2013, 02:14:40 AM »

Sloppiness in thread engagement is more to do with clearance, isn't it?
Surely variation between thread pitches on male and female components is bound to lead to thread tightening as more threads engage gradually taking up the clearance.

NeoTech · « **Reply #12 on:** April 11, 2013, 04:38:15 AM »

ah, well sure, my slop is not side to side though its "linear" in and out. But well most often when threading i found that slop side to side is a clearance issue.

steamer · « **Reply #13 on:** April 11, 2013, 08:42:59 PM »

Hey
I did a write up on doing exactly this a while back. Check out modelenginemaker.com under quick machine mods if i recall. I cut new threads for a W20 draw bar.

Davef

steamer · « **Reply #14 on:** April 11, 2013, 08:52:48 PM »

Nope
Look under metric transpostion gears

http://www.modelenginemaker.com/index.php/topic,649.0.html

Dave

steamer · « **Reply #15 on:** April 11, 2013, 09:53:37 PM »

With a quick change gear box and a 47/37 gear cluster, ( 1.27027) , set the lathe to cut 12 threads/inch

12 x 1.27027 = 15.2432 threads/inch = .065602 pitchX 25.4 mm/inch= 1.6663mm pitch........we can talk about the missing parts of a micron....but..

Dave

Pete. · « **Reply #16 on:** April 11, 2013, 10:51:36 PM »

Andreas, silly question but - you know - it has to be asked.

You have got your two different angles on the correct side of the thread haven't you?

NeoTech · « **Reply #17 on:** April 12, 2013, 01:26:16 AM »

Steamer; thats alot closer than i manage to calc it. I do have a metric lathe bit somewhere i there i should be able to figure it.

Regarding angles. Yes they are correct i learned that after the first attempt. So made a small block with the angles for holding the bit and a fence to square against.

NeoTech · « **Reply #18 on:** April 12, 2013, 03:50:06 PM »

Quote from: steamer on April 11, 2013, 09:53:37 PM

With a quick change gear box and a 47/37 gear cluster, ( 1.27027) , set the lathe to cut 12 threads/inch

12 x 1.27027 = 15.2432 threads/inch = .065602 pitchX 25.4 mm/inch= 1.6663mm pitch........we can talk about the missing parts of a micron....but..

Dave

I gotta ask a stupid question.. i sat down and tried todo the math on using a gear cluster, getting closer to my 1.666 desired pitch.. Im on a metric lathe with gearbox though.
When setting the machine to a 3mm pitch i have a 60/120/60 gearset in the machine originally. I have a hard time to calculate the gearset that are in the machine already.. adding a cluster didnt really help me wrap my brain around this.. Sometime i really regret to be stupid. ;D

steamer · « **Reply #19 on:** April 12, 2013, 08:25:38 PM »

You're not stupid.

My lathe is english...and I'm sorry I missed that part earlier.

However,

If your lathe is set to turn 3mm pitch, you need to add a cluster that will give you 1.6667...or nearly.

So...3 X = 1 2/3 or 3 X = 5/3. We need to solve for X

Divide both sides by 3 we get X = 5/ 3(3) = 5/9

So we need a cluster that has a ratio of 5/9 or 50 /90 or 25/45 or 20/36 or 15/27

In my case, I needed to make a wider spindle gear also ( same number of teeth...just wider) to put my cluster on. You may be able.....depending on your lathe.....to space the spindle gear out to do the same thing.

Do you have any gears that are at least close to the ratio's above?

What other pitches can you cut?....If you can cut 5mm and put a 3/1 cluster or set of gears...you get there too.

Dave

Pete. · « **Reply #20 on:** April 12, 2013, 11:53:15 PM »

I think your best bet is to list what change gears you have.

NeoTech · « **Reply #21 on:** April 13, 2013, 02:47:17 AM »

Well Pete, that would be one way.. But what would i learn by doing that? Its a little bit when i teach people using computers or programming. I provide the tools, the problem and a approach to solve the problem.. Not the solution. =)

Steamer so let me see if i get this right..
In my initial post i talked about the 1 2/3 ratio that occurs with a 1.666 pitch. And how i could recalculate it to use a weird gear setup.
What i really missed out that by doing that i shouldnt touch the initial 1:1 gear that is in there (60/120/60) but add a 4th gear group to the equation instead and calculate that gear cluster instead. It make a bit more sense actually. Now i will just need to code a phone app that does the gear calculations for me.. cuz im lazy.. ;)

steamer · « **Reply #22 on:** April 13, 2013, 06:51:40 AM »

Well....that's the jist of it. There are practical issues also. Physically getting a cluster in might be one of them...and I don't know your lathe.

I'm assuming it has a 3mm pitch leadscrew. What pitch is it?

It might be just that simple though....you should also look at compounding one of the gears in the train if you can, If you have a change gear lathe, you may be limited on how many you can add to the "banjo".

My turn for the dumb question....do you have a manual for the lathe,,,and does it have a chart of threads it will cut?....you might be suprised to find some odd balls.....maybe this one is one of them?

Dave

steamer · « **Reply #23 on:** April 13, 2013, 07:09:29 AM »

Or to put it Petes way....what change gears do you have?

Dave

NeoTech · « **Reply #24 on:** April 13, 2013, 11:24:31 AM »

I have this lathe; http://www.optimum-maschinen.de/produkte/drehmaschinen/d-320/index.html (yeap chinese crap clone slapped with german tag on it, holy crap this is a crappy machine).

And the large idler gear (120) is compounded with another gear. And the gear on the screw sits with a small bushing that can be fitted so it goes on the outside or the inside of the large compounded gear. I think this is mainly so i can switch between metric and imperial easier.

And i actually have no idea of what pitch my screw has. My lathe has a norton gearbox so i have been using that for calculations.

steamer · « **Reply #25 on:** April 13, 2013, 01:18:26 PM »

I checked your references...but no threading chart.....the fact is has a 120 tooth idler tells me it has some room to play with though.

What is the stud gear, the train and the screw gear in its normal setup?....does it only have the 120 tooth idler?

Dave

NeoTech · « **Reply #26 on:** April 13, 2013, 02:36:13 PM »

The normal gears in the machine is 60 / 120 / 60 and that covers like 95% of all the threads that can be cut on the machine. The 120 idler is paired with a 127idler in a "group".. when doing imperial i run the screw from the 127 and spindle on the 120 and well there some magic happens.. i rarely do imperial.

steamer · « **Reply #27 on:** April 13, 2013, 07:41:14 PM »

OK ..so in normal operation, the 120 tooth gear is just an idler...the input shaft turns the same speed as the spindle (60/60 =1)

60 x 5/9= 33.333.... so no love changing 1 gear.

If you can put a 50/90 cluster in between the 120 and the screw gear...step up in speed... your there.

so

(60)(120)(50/90)(60)....

I also suspect that you won't be able to use anything smaller than those gears...just because of space requirements.....due to the 120 tooth gear.

What gears do you have?
And

What DP or module are the gears?

Dave

NeoTech · « **Reply #28 on:** April 14, 2013, 03:15:55 AM »

I do have the 50 gear but not the 90 gear... i need to figure out what module my gears have so i can make a larger one.. I think have produced more "extra" tools with my tools than actual projects since i got these machines.

awemawson · « **Reply #29 on:** April 14, 2013, 03:45:44 AM »

That is the entire justification for my workshop - to make tools to mend tools

Not sure if the swarf is a byproduct or possibly the main product

Swarfing · « **Reply #30 on:** April 14, 2013, 04:25:11 AM »

Whats the outside diameter of your 120 gear and 50. Your lathe looks a similar size to mine which is a 1.25 mod. You can check the size of your gear against the HPC website as they stock standard mod gears in all sizes.

NeoTech · « **Reply #31 on:** April 14, 2013, 04:55:19 AM »

What is the HPC site??? =)

Swarfing · « **Reply #32 on:** April 14, 2013, 05:24:13 AM »

http://www.hpcgears.com/

Swarfing · « **Reply #33 on:** April 14, 2013, 05:33:01 AM »

I just tried looking up the spur gear it does not show online so you need to download the catalogue first. For an example though a 1.25 MOD 120 teeth gear O/D = 152.5mm.

If you can't see it let me know what size yours is and i can look it up in the book i have

steamer · « **Reply #34 on:** April 14, 2013, 09:45:59 AM »

Well Andreas....I made the cluster for my lathe....got where I needed to be eventually....

I needed to make a cutter arbor for the gear cutter I bought...then I needed to make a gear arbor to hold the blanks...then modify the dividing head tailstock I had because the height didn't match the dividing head....then set it up..

its a fatal disease...there is no known cure.....

NeoTech · « **Reply #35 on:** April 14, 2013, 10:49:09 AM »

Wonderful hobby isnt it... No wonder my air rifle never gets finished. ;D

NeoTech · « **Reply #36 on:** April 19, 2013, 05:02:17 PM »

So i need to cut a 90 tooth gear it has the module of 1.25, that would mean i would need to make a hob.. Or get me a gearcutter.. im a cheapskate and a hob seems interesting...

Anyone here ever made a straight cutting hob? I have seen alot of people making hobs out of different acme screws and what nots...

My main issues with hobbing is this..

1) Distance between each tooth according to the Module 1.25.
2) Does it matter how many teeth you will cut if you use a hob? (Im pretty sure it doesnt matter
3) The depth of the tooth can be calculated by doing 3.14159 * Mod (1.25) == 3.926mm (or am i completely off now?)

NeoTech · « **Reply #37 on:** April 19, 2013, 05:16:13 PM »

Uhm.. i made a rack in Solidworks and checked the tooth depth.. So the distance between tooths is 3.14 * module. ..

But it seems at a Module 1, the depth of the tooth is 2.25.. i cant reverse or derive this number (and i need to understand why its 2.25).

steamer · « **Reply #38 on:** April 20, 2013, 12:42:47 PM »

I think its Ivan Laws book. GEARS AND GEAR CUTTING shows how to make your own flycutters for making gears

Dave

vtsteam · « **Reply #39 on:** April 20, 2013, 10:36:11 PM »

For flycutting gears:

Making gear cutters with taper drills:

http://mikesworkshop.weebly.com/making-gear-cutters.html

(See also 2 updates and improvements on the method at Mike's workshop site.)

Cutting gears:

http://www.deansphotographica.com/machining/projects/109/gears/109c.html

John Stevenson article:

http://www.metalwebnews.com/howto/gear/gear1.html

Hobbing with rack type hob:

http://www.jeffree.co.uk/pages/multi-tooth-gear-cutter.htm

hopefuldave · « **Reply #40 on:** April 21, 2013, 03:23:43 PM »

Quote from: NeoTech

Uhm.. i made a rack in Solidworks and checked the tooth depth.. So the distance between tooths is 3.14 * module. ..

But it seems at a Module 1, the depth of the tooth is 2.25.. i cant reverse or derive this number (and i need to understand why its 2.25).

Uh huh, the pitch of a rack ( or a worm...) is "unwinding" the teeth, so going from diameter of the pitch circle to the circumference means multiplying by Pi, for metric module pitches, mod times Pi, but for "English" DP divide Pi by the DP, simples

so for your 1.25 mod hob, you need the "teeth" to repeat at Pi Times 1.25 mm.

The depth of cut, 2.25 x mod, is because an involute gear needs clearance at the bottom of.the tooth space, in an ideal world the cut would be 2 x mod, but that leaves no room for grease, grit, badly-formed teeth...
On larger gears, the clearance can be less, as there's more room to play with, so for a 5 mod it could be reduced to 0.125, giving q cut of 2.125 times the mod, or less.

So... Your hob needs teeth pitched at Pi x Mod, with an included angle of twice the pressure angle, and a depth of 2.25 x Mod. This won't be a "topping" cutter, as far as I can tell, so the gear blank will need to be the correct diameter ( teeth+2 x Mod)...

Hope that makes.sense!

Dave H. (the other one)

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Author Topic: Revisiting the buttress thread. (Read 14884 times)