[modeleng] Re: Calculating gear form of very low tooth count gears

Hi,

I've just built a gadget similar to a dividing head for my mill to cut 
gears. I've written an excel sheet to calculate the gears, teeth turns 
of the knob, degrees per tooth and the od of the disk needed for any 
gear from 10teeth to 150+. Above 150 I just need to extend the 
worksheet. Cutting plastic is almost as easy as metal....just sandwich 
it between two identical sized metal disks to give support to the 
plastic disk.

Today I witnessed the death of an engineering workshop. I was offered 
any metal bar I wanted from a small works that has closed and was being 
cleared. I took two loads of bar from 3mm to 50mm thick in round, square 
and hex in 3m lengths. Probably totals about 100 to 150 lengths so 
should keep me going for a while. While I was loading my car they were 
forklifting BSA capstan lathes into skips to be scrapped. This works had 
over thirty of them. Several welders capable of over 500 amps and a 
large amount of 'supporting' machinery and spares. Gearwheels by the 
bucket load for the capstans and all the metal bar I could not take. I 
probably only took less than a twentieth of what was there. I have my 
name on four pillar drills which are still in use for the next few weeks 
finishing a contract. All 3phase but will swap the motors. They are all 
over 40 years old and built like battleships. Several weeks ago they 
gave me a benchmaster Senior mechanical saw which is now cleaned, 
painted and adjusted. Works well with a three quarter horse 2ph motor 
for 50 quid from machine mart. Cuts 30mm bar in six minutes without 
cooling (available on the machine when needed). I spoke to the guy who 
is clearing the works. The owner who was his friend has died and he is 
clearing it for the widow. I offered to get G&M machines or someone 
similar to buy and collect the machines he scrapped but he said he could 
not spare the time and urgently needs to clear the unit. I think it's a 
crying shame these are going the way of hundreds of other 
machines....scrapped through lack of interest or care.


Julian.













Alan Stepney wrote:

>At recent Midlands ME exhibitions I have picked up several 12 v motors. The 
>next one (ME exhib) is coming up shortly so that could be a (another!) good 
>reason to go.
>
>As for the gears, gear cutting of the larger ones in metal isnt too hard, 
>but I imagine that plastics, depending upon the type used, might make life 
>difficult.
>Can you not search round for something that will do the job?
>This seems to be a case where a comprehensive "odds" box is worthwhile!
>
>You can often find small gears in laser printers, 5 1/4" floppy drives, and 
>similar older computer items.
>http://www.alanstepney.info
>Alan Stepney's Model Engineering, steam, and workshop pages.
>
>
>----- Original Message ----- 
>From: "Chris Crosskey" <chris.crosskey@xxxxxxxxx>
>To: <modeleng@xxxxxxxxxxxxx>
>Sent: Tuesday, September 25, 2007 9:40 PM
>Subject: [modeleng] Calculating gear form of very low tooth count gears
>
>
>Hi Folks,
>I'm trying to clone a very small gear for a slightly off-beat lighting
>project. I'm trying to clone an Optikinetics Total Eclipse (see
>http://www.funky-parrot.com/totaleclipse.html for more info about this
>rather insane lighting effect), and I've run into two problems, one of
>which is the motor, it's probably about 8W, 12V AC and runs fairly fast,
>the other is the sun gear in its planetary gear arrangement is 8-tooth
>and it has a hole up the centre, it's about 8mm wide (the gear overall)
>so it might well be 1Mod. If I could work out the profile without
>measuring a rather worn one in my possession and trying to copy it it
>would be very helpful. Is it worth measuring the planet gears (about
>25mm/25 teeth but I'm not being precise here)... it could just as easily
>be 24DP, I will need to measure properly, but how would I go about
>cutting such a gear?.... is there a way to generate a cutter for
>this?... I've got the WPS book on gear cutting (one of Ivan Law's IIRC)
>and I'm happy enough cutting other, rather higher toothed gears but I'm
>not up to working it all out at those kind of levels.... Assuming it is
>1 Mod then what sort of pressure angle will get me in the ballpark for
>an 8-tooth gear with a 2.5 to 3mm hole in the middle of it?....
>The effect works by having a pair of rather inefficient drive systems
>from a single motor powering up both sides of a planetary gear system
>where the gears are clear and have colour section son them. The whole
>assembly is spinning so fast that it just colour mixes in graduated
>bands that change due to differences in the inefficient power
>transmissions (these can be varied by moving one of the foam covered
>jockey wheels BTW)..... I'm thinking of cloning it without the
>inefficient drives and just having a one-tooth variation in a normal
>gear transmission system..... hopefully a 12V 500rpm sync motor will run
>the whole thing fast enough to colour blend..... but I'm still stuck
>with that minute gear in the middle of the planetary, if I go small
>enough on the tooth form to get into sensible territory I'm down at 0.5
>Mod and I'd rather not be cutting gears that fine in plastic then
>whirling them round in the gate of a projector..... I guess I could try
>it though.......
>
>Any thoughts on 12V AC motor sources would be welcome too, I've done
>some googling but not turned up anything particularly useful.... And
>Optikinetics (and their main dealers Optifanatics) have been very
>helpful but simply don't have much information (or indeed spare parts)
>for stuff that old.... plus the original designer (who was mad as a box
>of frogs) died a fair while ago.....
>
>Any help gratefully received
>
>Chris Crosskey
>
>
>________________________________________________________________________
>This e-mail, and any attachment, is confidential. If you have received it in 
>error, do not use or disclose the information in any way, notify me 
>immediately, and please delete it from your system.
>________________________________________________________________________
>MODEL ENGINEERING DISCUSSION LIST.
>
>To UNSUBSCRIBE from this list, send a blank email to,
>modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject 
>line.
>
>
>  
>

MODEL ENGINEERING DISCUSSION LIST.

To UNSUBSCRIBE from this list, send a blank email to, 
modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.

Other related posts: