GENERAL INFORMATION

MODIFYING MECCANO GEARS & PINIONS - PART 1

© MIKE DENNIS 2001

 

 

The main reason for modifying gears and pinions is that Meccano gears and combinations occupy too much linear space due to the bosses. A valid second is excessive face width.  Both factors impose unnecessary restrictions on what can be built especially to smaller scales.

There is no reason why Meccano gearing should not follow common engineering practice.  For example double gears are not new.  The No1 clockwork motor provides some.

‘Double gears’ using any combination are feasible, although I accept 1/2" or 1" pitch is the most desirable.  Modified gearing and associated parts become dedicated equipment so they should ideally be made in pairs or fours and recorded in Meccano stock lists as modified parts.

The first ‘double gear’ combinations I made, shown below, were based on the most common gears as they are readily available second hand.

The same size Plastic gears can be altered similarly.
 
 

BASIC GEAR MODIFICATIONS

 

Figure 1           19/57T 

A -> drill and tap 10B.A., fit screw, cut and machine flush with the gear face. 

This prevents the gear from turning 
  

Both types can be made with a pinion face width of 6mm or 4mm.

Figure 2         25/50T


 
 

PINION MODIFICATIONS

Standard gears and pinions restrict what can be made as they are basically designed for general purposes.
They all have bosses that take up far too much linear space, especially in gearboxes and in reduction gearing where space is limited.

The following modifications greatly increase potential use when linear space is restricted and have no detrimental effect on performance in normal use. Fig 1 shows a sectional drawing Left, as a view on the Centre Line in direction of arrow A detailing a full set of modifications which can be carried out on all PINIONS as listed.  Plastic 19T pinions and all Brass 19T and 25T pinions.  Note: All 15T and 11T pinions can be grooved and slotted only.

Figure 3

Key:
CB - Counter bore Flat Bottom drilled Ø 3/8"clearance x 1/8" deep for closer gear cluster potential.
G - Gap Machined 1/16" wide to Ø 7/32" (0.218") for selector strip as shown in Fig 4
S - Slot - Cut by hand and filed or machined in boss face for use with a male dog clutch, Part No 144a.
 
 

SELECTORS

Any strip, narrow or standard can be modified as a selector.

Figure 4
 
 

REVERSING PINION CLUSTERS

These can be made from 2 pinions of the same diameter,  normally with 11,15, or 19 Teeth.  One pinion is counter bored Ø 7/32" x the boss length, while the other has a shoulder machined to the boss length with its Diameter to suit the counter bore.

They are designed to operate across the face of 50T Contrate gears with a central neutral position.

Note: If used on 25T Contrate gearing they should have the face width reduced to 1/8" to provide sufficient clearance and grub screws in both situations must be sub-flush to clear the Contrate gear boss.

Referring to the drawing,  Fig 5, the gap G is formed naturally but may have to be widened for thicker gauge strips.  This is done by machining the back face of the right hand pinion until a 1/16" wide gap is achieved for the selector.

Figure 5
 

All cluster gears shown can be used on either Tri axles as shown or on keyway rods.  Grub screws and key bolts should be super glued or fixed with engineering adhesive to ensure free sliding fits and if key bolts are used on reversing pinions the heads should be filed off to clear the central boss in the Contrate gear, as reversing pinions are dedicated for special use!
 

The drawing below is based on an original by Phillip Webb in the HTMC Newsletter Autumn 2000. I developed the 11T Zinc Double pinion conversions for compact reversing gears and used them on ‘Aggravator’, my Micro Block setter crane.

Figure 6 -- 11T REVERSING PINION

For use with 25T Contrate gears

A - Left hand pinion - Ø A 7/32" (0.218") Drilled x 7/32" Deep as shown.
B - Right hand pinion Ø A x 9/32" long as shown  (0.28") turned to produce a light press fit in A
C - Grub Screw. This must be Loctited or super glued in position and sub-flush in the pinion boss.  The assembly must be a free sliding fit on the tri-axle D and the boss must clear the centre of the 25T Contrate gear E.
The overall dimension of the double pinion assembly must not exceed 17/32" (0.531")  to satisfactorily provide a central neutral position as shown on the Right hand side of the drawing and the operating gap for the selector F must not be less than 1mm (0.040")
F - Selector .The selector shown is based on a 5 hole narrow strip but it can be made to suit requirements and is not supplied with reversing pinions.

MULTI RATIO PINION CLUSTERS

Double gear combinations are not new in Meccano as the No1 clockwork motor proves.  Why not make them for ourselves as any combination can be used although meshing at 1/2" and 1" spacing is the most desirable for general use therefore the most common will be 2:1, 3:1 and 4:1 meshing with 50T, 57T, and 60T gears respectively.

Fig 7 Below, shows a 19T /25T pinion double gear combination but 15T/19T or 15T/25T combinations can also be made using the same technique described previously.  The pinions are shown in standard form but can be counter bored on the faces if desired. They should not have grooves machined in the boss.

Figure 7

The gap, G, is achieved by the same
method described previously.
 
 

CLUSTER GEARS USING THE No 31 GEAR

Key to drawing Fig 8, Below.
A - No31 - 38T gear. The face is reduced to 5mm from the boss side to allow the groove to be machined in the boss with sufficient clearance from the
screw holes.  The gear is then bored through 1/4" Dia.
B - The Pinion can be 25T x 1/4" face or 25A, 19T 26, or 26A, or a 15T x 1/4" face 26B. These are machined to a light press fit with the bore of the No31 gear so that the screw holes are in line when fitted.
C - Counterbore - Ø 3/8" Clearance for boss when used in close proximity..
G - Gaps 1/16" Wide to Ø 5/16" Note: After machining the groove to the correct diameter the pinion should finish with 5mm face width approximately.


Note: Selector should be made similar to Fig 4 but from a standard strip with the open slot 5/16" wide.

The drawing shows a slot in the boss but this optional as it can be machined or cut and filed by hand when needed.

Figure 8
 
 

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 be beaten by minor metric problems caused by the ‘enemy’!

SOME SOLUTIONS
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.
2. If a 13T pinion is used with a Zinc 25T they mesh at 1/2"pitch which is a far more satisfactory 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 1.125" long special threaded pins from 1/4" A/F Brass for more than one double gear and greater reduction.

Figure 9 - 11/25T & 13/25T double gears

13/25T double gears work at standard pitch.
Face width of the pinion section is 4mm (0.157") approximately.
 
 

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