Broach classes

[DalboyParticipant @dalboy]

Not sure if the title is right.

 

I am after a 1/8″ broach but when looking at them there are two options either A or B type can anyone enlighten me to the difference.

Thanks in advance

[Ian HewsonParticipant @ianhewson99641]

Hi Dalboy

If it’s for the flywheels on your Farm Boy, try Arc’s metric broach’s and make your own guide up for the imperial shaft. Worked well on mine.

Usefull guide to broaching on the site also.

Ian

[JasonBModerator @jasonb]

The class letter refers to the width of the “spine” so an 1/8″ Type A will have a 1/8″ spine and fit into bushes with a 1/8″ slot.

Type B at 1/8″ will have a 3/16″ spline and fit into a 3/16″ slotted bush.

If you are generally going to be making models of this sort of size then I would go with type A as that allows for smaller bushes and therefore smaller shafts so you can do 1/16″ and 3/32″ keyways as well as 1/8″ all with the same bush Which should cover you for shafts from 1/4″ dia to 1/2″

[Brian WoodParticipant @brianwood45127]

Helpful information Jason, thank you for explaining the difference.

Regards   Brian

[Ian Hewson]

On Ian Hewson Said:

Hi Dalboy

If it’s for the flywheels on your Farm Boy, try Arc’s metric broach’s and make your own guide up for the imperial shaft. Worked well on mine.

Usefull guide to broaching on the site also.

Ian

Yes it is for the Farm Boy I have already cut the keyway on the crank to 1/8″. I have been out of the workshop due unforeseen circumstances but hope to be back on it very soon.

 

On JasonB Said:

The class letter refers to the width of the “spine” so an 1/8″ Type A will have a 1/8″ spine and fit into bushes with a 1/8″ slot.

Type B at 1/8″ will have a 3/16″ spline and fit into a 3/16″ slotted bush.

If you are generally going to be making models of this sort of size then I would go with type A as that allows for smaller bushes and therefore smaller shafts so you can do 1/16″ and 3/32″ keyways as well as 1/8″ all with the same bush Which should cover you for shafts from 1/4″ dia to 1/2″

Thank you Jason sounds like a good explanation and suggesstion to which one to go for.

[Ian HewsonParticipant @ianhewson99641]

You could “fit” the key, it’s only 7thou difference.

Depends on the cost and availability of an 1/8 broach.

Ian

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