7mm Loco hornblock cutouts, what size?

[bluestag]

I'm getting ready to build a 7mm loco kit; it has milled frames for a rigid chassis.    No indication of cutouts for hornguides.   I intend to build it with a compensated chassis, but I don't know the standards for such cutouts.    How high above axle height is the cutout supposed to be?    How wide is the cutout supposed to be?   Are there any etched hornguides on the market?   

Edited January 6, 2020 by bluestag

[sagaguy]

Slaters can supply sprung axle boxes with gunmetal horns.The centre of the cut out will be determined by the measurement of the coupling rod crankpin holes,the cut ot size will be determined by the horn guide.

 

                     Ray.

[Simond]

Here are some diagrams somewhere, and it does depend on the make of hornblock/hornguides, but as sagaguy says, the vertical centrelines depend on the coupling rod centres, the horizontal centreline is driven from the general assembly.  
 

because you need some tolerance for assembly, you must cut the slots slightly wider than the hornblocks.  Some hornguides have features which locate them vertically, so a fixed offset above the horizontal centre line is needed.

 

neither of which answers your question “how big?”  

 

look at your (and other makes of) hornguides, look on Slater’s website, and on google, and if you can’t find it, I’ll look at my records after work.

 

atb

Simon

[Hal Nail]

 

13 minutes ago, Simond said:

look at your (and other makes of) hornguides

Rolling (pun genuinely not intended) back to the OP, I think the critical bit is don't cut anything until you've actually bought the hornguides?

 

Sorry if I'm stating the obvious or missing the point but better it is me that looks foolish!

Edited January 6, 2020 by Hal Nail

[sagaguy]

I used Slaters sprung axle boxes on my DJH 7mm Fairburn tank kit.I didn`t intend to at first but the chassis rocked on the centre drivers so it was a case of having to take the plunge.I was lucky in having a milling m/c but the main job was keeping the chassis square. lengths of 3/16" silver steel was inserted into the centre & front bushes & the lines for the horns were very carefully marked out from the centre of the front length of silver steel & then the slots were milled leaving the final few thou filed out to fit the horns.If i ever build another 7mm loco kit,i`ll fit sprung axle boxes before i assemble the frames.You can just about see them in the pic.

 

                       Ray

Edited January 6, 2020 by sagaguy

[bluestag]

Yes, I understand that the center line is determined by the prototype and the coupling rods.   The frames have bearing holes bored thru, I suppose I can measure a hornguide and measure half the distance plus a bit for play.    What I am really looking for is the height of the cutout.  In 4mm it is standardized.   I had assumed it would be in 7mm as well.

[sagaguy]

The horns should be level with the bottom edge of the chassis because you have to fit the axlebox retainers across the bottom to stop the boxes falling out!.

 

                            Ray.

[ROSSPOP]

11 minutes ago, bluestag said:

Yes, I understand that the center line is determined by the prototype and the coupling rods.   The frames have bearing holes bored thru, I suppose I can measure a hornguide and measure half the distance plus a bit for play.    What I am really looking for is the height of the cutout.  In 4mm it is standardized.   I had assumed it would be in 7mm as well.

 

I modelled in 4mm for thirty years and I don`t recall cutout heights being standardised !!!!????

 

Your cut out height will be dependent on the design of your chosen hornguides and you keeping to the axle hole positions in the chassis frame so that your loco ride height is correct for the design of kit and the position of the wheel in relation to the wheel splashers...….,

 

Good kits have the axle centre line pre-etched...……. here is my working out allowing for the hornguide spring to be fully compressed....

 

 

 

These are the measurements for Slaters hornguides before cutting...…..

 

 

 

Hope this helps

 

 

[markjj]

Slaters hornbock dimensions are on the back page of their price list which is downloadable on their website.

[bluestag]

4 hours ago, ROSSPOP said:

 

I modelled in 4mm for thirty years and I don`t recall cutout heights being standardised !!!!????

 

Your cut out height will be dependent on the design of your chosen hornguides and you keeping to the axle hole positions in the chassis frame so that your loco ride height is correct for the design of kit and the position of the wheel in relation to the wheel splashers...….,

 

Good kits have the axle centre line pre-etched...…….

 

 

Well, trust me, there is a standard height above axle centerline that the cutouts should be in 4mm.    All the etched hornguides will nestle up to that top in the frame cutout and give you good up and down movement of the axles.

 

This kit, while good, is 30 years old and has milled frames, not etched.  So there is obviously a center line where the axle bearings are supposed to be, but it is not marked.

 

I was hoping there was a standard height for the cutouts in 7mm but apparently not.

[bluestag]

1 hour ago, markjj said:

Slaters hornbock dimensions are on the back page of their price list which is downloadable on their website.

Thanks, I'll go look.

 

I favor etched fold up hornguides, who makes them in 7mm?

[bluestag]

1 hour ago, markjj said:

Slaters hornbock dimensions are on the back page of their price list which is downloadable on their website.

"7960B and 7960C (new type) fits slot in frame 10.5mm wide, with top of slot 7.5mm above centreline"

 

Thanks.   I can work with that!

[sagaguy]

It`s the axle centres that are the most important dimension.

 

                         Ray.

[JeffP]

14 hours ago, bluestag said:

Thanks, I'll go look.

 

I favor etched fold up hornguides, who makes them in 7mm?

Slaters used to as well.

I know Finney 7 do, both LMS and LNER types.

[bluestag]

16 hours ago, sagaguy said:

It`s the axle centres that are the most important dimension.

 

                         Ray.

Yes, but if you don't get the hornguides roughly centered in the vertical on the axle line, then you may not have appropriate vertical movement.   Hence my question.