11T AND 25T PINIONS AND GEARS
Everyone who has tried to use them knows
that the French 25T and 11T Zinc gear and pinion (F 25C and 26n respectively)
do not mesh properly at 1/2" centres and are prone to slip under load.
They mesh at 12mm (0.472") and one reason is that the OD of the 25T gear
is about 1/2 mm (0.020") smaller than standard 25T brass gears! English
model engineers are not willing to beaten by minor metric problems caused
by the 'enemy'! The basic rule for Meccano gearing which is 38DP is that
if the total number of teeth on any two adds up to 38 they will mesh correctly
at 1/2" pitch therefore an 11T pinion would need a 27T gear.
1. Standard 25T brass gears can be faced off to a 2mm face width (0.08") and these are slightly better for compact reduction gearing if a threaded pin is used as the lay shaft.
2. If a 13T pinion is used with a Zinc 25T they mesh at 1/4"pitch which is an all Meccano solution.
3. 11T and 25T Zinc gears can be meshed
by using the standard threaded pin as a lay shaft, taking advantage of
the undercut beneath the integral nut to reduce the pitch to 12mm and locked
in place. There is sufficient play in Meccano holes in plates and bush
wheels to do this. I have also made 1 1/2" long special threaded pins from
1/4" A/F Brass for more than one double gear and greater reduction.
11T &13T DRIVE PINIONS
Slot details: 1/16" wide x 1/16" deep.
Note:- The unit shown below is driven by
the pinion as shown in
the sketch via a 'slug' shaft cut from an axle rod 4.1mm OD x 1/4" long
bored to Ø 2mm and with a slot as stated.
11/25T PROTOTYPE 4 STAGE FLAT UNIT
The double gears are on two lay shafts either side of the main shaft to give a pitch of 12mm 1/4" A/F x 3/4".
Hexagonal brass spacers are used on this unit which was one of my first experimental drives for the TBM drive module.
Allen bolts are used through out except for motor retention.
The Drive motor is a Swiss mini-motor driving the slotted 11T pinion described above.
The motor shaft is 2mm Diameter so the
pin in the motor shaft drives a 1/4" long slotted 'slug' shaft and the
Below is another Sketch of 11/25T gear as used in units shown in the prototype unit above.
13/25T double gears work at standard pitch.
Pinion face width is 4mm (0.157") Approximately.
WORKING EXAMPLES FEATURING 11/25T & 13/25T DOUBLE GEARS.
Swiss Mini-motors are supplied by Motors Direct.
The two examples below show 13/25T double gears used in reduction units. The front Bearing plates are standard 8 hole Bush wheels with the 2 stage using 3/4"long hexagonal threaded spacers while the 6 stage uses 1/4"square x 1" special threaded spacers designed for multi purposes and both types are used to eliminate nuts.
The motor mounts are bush wheel conversions
used in Swiss motor mounting kits. No parts are altered as 13/25T double
gears work at normal 1/2"spacing. 13/25T gears mesh at standard spacing,
therefore standard parts can be used.
Two stage 13/25T unit
Six stage 13/25T reduction gear unit
11/25T DOUBLE GEAR REDUCTION DRIVE UNIT
Another view of the first experimental
11/25T 4 stage reduction gear unit.
The first and third double gears are made from Zinc 26n and F25C pinions and gears which run on old style threaded pins with integral nut as layshafts. These are No2 strip conversions and the undercut beneath the nut allows the pins to be moved in the mounting holes for the gear to mesh at 12mm centres.
The second double gear is placed on a 11/2" long output shaft just forward of the drive pinion (centre) while the final standard F25C provides the 4th stage of reduction.
The threaded spacers are 3/4" long 1/4" A/F hexagonal brass to eliminate the use of nuts. The frames are two converted No5 strips with a special 0.65" O.D. brass boss with 10mm bore on the rear for the motor mounting in the centre hole.
A removable sleeve piece (not shown) fits
fairly tightly on the OD of the boss to enclose the motor. The front frame
is fitted with a standard size boss in the centre hole to act as a substantial
bearing for the output shaft.
The output pinion is a 16 DP 167C driving a 96T Delrin gear ring for the cutting head. The front plates are Mecarep 74 conversions with a central boss and a slotted top centre hole for the lay shaft.
A long threaded pin is used for the lay shaft and the collar is an Aero type. 12 Threaded spacers 0.9" long were made for the 6 drive units. Four are non-working assemblies and the motor mounts are Mecarep Swiss Mini-motor kit parts shown on page 13.
The initial drive is by a 1/4" long hollow
'slug' shaft for the motor shaft pinion which is driving three 13/25T double
gears and a final standard F25C.
The TBM drive unit
BRIEF COMMENTS ON MECCANO AND OTHER LARGE TOOTHED GEAR SYSTEMS
The illustration shows a view inside the drive module of my 1/35 scale South land running Channel tunnel boring machine. The actual machine had 6 reduction /motor drive units.
ThThe top 4 units in the model are non-working while the lower 2 provide power to a 96T Delrin Gear which will eventually drive the cutting head as on the prototype which is at Folkestone.
The model is still under construction and
keen observers will note the modified 167b flanged rings.
The 'extra' holes are for rams and other parts!
The 96T Delrin (Polyacetal 150) gear is 16DP and was machined from a purchased item. The No 167 Meccano series gears and quadrants are 16DP and all but the quadrants have existed since the 1920's.
Exacto (Argentinian Meccano) uses 20DP gears so there is no reason why others cannot be privately developed for use with both ranges. I have gone a stage further by developing a series of heavy duty parts involving a 4 in 1 system from 1/2" downwards to 6mm diameter shafting and this system is covered in part two.
I have also developed a 1/4" pitch sprocket
& roller chain system to compliment it which is more realistic than
standard Meccano. All bosses are 1/2" Diameter which provide sufficient
wall thickness for the screw thread.
MODEL ENGINEERING TIP
Many older commercial small 'back geared' centre lathes used 16DP for screw cutting change wheels so these can be adapted for use with Meccano by making an interchangeable boss. Odd gears and even sets of change wheels are available at most second hand machine tool dealers so take a 16DP Meccano 167c pinion along with you to check the meshing.