Punch Grinding Advice

[Colin H]

Morning All, I’m part way through head rebuild on motorcycle and have some valve seat cutting equipment on the way. Like most of them it uses a guide that slides into valve guide to cut seat concentric with newly reamed guide bush.

I want to be able to grind my own guide pins so looking at options between a pinch grinding spinning body like this.

Or this other style which I think will reduce what material I can hang
out the back.

Or a simple spin indexer like this.

I know nothing about punch or cylindrical grinding so would welcome advice on accuracy and usability of the above. I have rotary table and indexing head so those abilities are not of extra use elsewhere.

Final option is grinding head in lathe but havent measured concentricity of my spindle I can’t imagine it being great.

 

[Brad93]

Morning All, I’m part way through head rebuild on motorcycle and have some valve seat cutting equipment on the way. Like most of them it uses a guide that slides into valve guide to cut seat concentric with newly reamed guide bush.

I want to be able to grind my own guide pins so looking at options between a pinch grinding spinning body like this.

View attachment 471860

Or this other style which I think will reduce what material I can hang
out the back.

View attachment 471861

Or a simple spin indexer like this.

View attachment 471862


I know nothing about punch or cylindrical grinding so would welcome advice on accuracy and usability of the above. I have rotary table and indexing head so those abilities are not of extra use elsewhere.

Final option is grinding head in lathe but havent measured concentricity of my spindle I can’t imagine it being great.

The first one is a proper punch grinder - GrindAll or Harig is what you'll find them under.
£1500-2000 for one of those.

Michelin is a chinese manufacturer of very very good copies.

A 5C style spin indexer won't have the TIR nor the roundness precision. You'll get oval/lobed parts

 

[Brad93]

Never seen the vertex style thing.

If you can grind between centres then a mayform cylindrical grinder attachment (or other brands, brown and sharpe made one) would work

 

[Agroshield]

Could you give some idea of the diameters and length (and ratio of the two, i.e. slenderness) you require.

That will have an influence on the most suitable equipment.

For purely cylindrical work, the Harig-type could be somewhat overkill in functionality, so you'd be paying for features you do not use. It has rotational stops on it and the vee-block is adjustable for off-centre grinding.

 

[Colin H]

The first one is a proper punch grinder - GrindAll or Harig is what you'll find them under.
£1500-2000 for one of those.

Michelin is a chinese manufacturer of very very good copies.

A 5C style spin indexer won't have the TIR nor the roundness precision. You'll get oval/lobed parts

Thanks for the reply. Yes I thought the indexer may be a little course for this type of work, just hopeful of being a cheapskate I think

The centreless style grinder doesn’t seem used in industry so that may be a clue to how good it is then.

I think the punch grinding head you mentioned may be way to go but will have to be cheap copy so thanks for the name of good copy

 

[Colin H]

Could you give some idea of the diameters and length (and ratio of the two, i.e. slenderness) you require.

That will have an influence on the most suitable equipment.

For purely cylindrical work, the Harig-type could be somewhat overkill in functionality, so you'd be paying for features you do not use. It has rotational stops on it and the vee-block is adjustable for off-centre grinding.

Thanks for reply, the valve cutting heads use around 10mm rod then grind down end to valve guide. I think the rods are around 300mm in length but ground section only needs to pass through guide I think. In that regard the reduced section only needs to be 40mm or so but many of the guides have really long sections. Although engine building seems to range from some decent tolerance work to country mile tolerance.

 

[Agroshield]

You do not say what machine you will be mounting the fixture on (i.e. how you will turn the abrasive wheel).

We have 40mm long, 10mm parent diameter, overall length of 300mm. What is a typical reduced diameter?

That is a minimum slenderness ratio of 4 at the parent diameter. Hence, any device that might include a tailstock as part of the package (or as a purchasable accessory) might be high on your list. However, you would not mount an indexer and tailstock parallel to the y-axis of a surface grinder.

Providing you have the space to mount it, I would not discount the spindexer (which has a tailstock available) without (a) researching to see if any TIR figures are available (e.g. https://www.arceurotrade.co.uk/Cata...ns-5C-Indexing-Head-with-ER32-Nut-and-Adaptor See also figures on Gloster Tooling one); (b) buying one with prior agreement of the seller that you will test these claims and return if it does not shape up.

The concentricity of your lathe is slightly immaterial. Dial the work in using a 4-jaw chuck, align the tailstock nicely and use a toolpost grinder. The accuracy will be more a function of the condition of the ways.

If this is for non-professional use, why do the pins need to be ground at all? You would only grind if the item is hardened and cannot be turned. Turning and lapping might be an alternative approach. If you really needed a hardened item, you could use silver steel for the pins, turn slightly over, harden, temper and then lap to final size. Sure, if you had to do 50 heads, all the same, a guide pin that is not going to wear out is the right way to go, but if the pin only needs to survive one head and then the next head, in a year's time, needs a different size anyway, other approaches might be more suitable.

 

[Brad93]

You do not say what machine you will be mounting the fixture on (i.e. how you will turn the abrasive wheel).

We have 40mm long, 10mm parent diameter, overall length of 300mm. What is a typical reduced diameter?

That is a minimum slenderness ratio of 4 at the parent diameter. Hence, any device that might include a tailstock as part of the package (or as a purchasable accessory) might be high on your list. However, you would not mount an indexer and tailstock parallel to the y-axis of a surface grinder.

Providing you have the space to mount it, I would not discount the spindexer (which has a tailstock available) without (a) researching to see if any TIR figures are available (e.g. https://www.arceurotrade.co.uk/Cata...ns-5C-Indexing-Head-with-ER32-Nut-and-Adaptor See also figures on Gloster Tooling one); (b) buying one with prior agreement of the seller that you will test these claims and return if it does not shape up.

The concentricity of your lathe is slightly immaterial. Dial the work in using a 4-jaw chuck, align the tailstock nicely and use a toolpost grinder. The accuracy will be more a function of the condition of the ways.

If this is for non-professional use, why do the pins need to be ground at all? You would only grind if the item is hardened and cannot be turned. Turning and lapping might be an alternative approach. If you really needed a hardened item, you could use silver steel for the pins, turn slightly over, harden, temper and then lap to final size. Sure, if you had to do 50 heads, all the same, a guide pin that is not going to wear out is the right way to go, but if the pin only needs to survive one head and then the next head, in a year's time, needs a different size anyway, other approaches might be more suitable.

Runout and parallelism is +/- 20 microns.
Thats a country mile in grinding terms

A GrindAll is in the realm of 50 millionths of an inch

 

[Colin H]

You do not say what machine you will be mounting the fixture on (i.e. how you will turn the abrasive wheel).

We have 40mm long, 10mm parent diameter, overall length of 300mm. What is a typical reduced diameter?

That is a minimum slenderness ratio of 4 at the parent diameter. Hence, any device that might include a tailstock as part of the package (or as a purchasable accessory) might be high on your list. However, you would not mount an indexer and tailstock parallel to the y-axis of a surface grinder.

Providing you have the space to mount it, I would not discount the spindexer (which has a tailstock available) without (a) researching to see if any TIR figures are available (e.g. https://www.arceurotrade.co.uk/Cata...ns-5C-Indexing-Head-with-ER32-Nut-and-Adaptor See also figures on Gloster Tooling one); (b) buying one with prior agreement of the seller that you will test these claims and return if it does not shape up.

The concentricity of your lathe is slightly immaterial. Dial the work in using a 4-jaw chuck, align the tailstock nicely and use a toolpost grinder. The accuracy will be more a function of the condition of the ways.

If this is for non-professional use, why do the pins need to be ground at all? You would only grind if the item is hardened and cannot be turned. Turning and lapping might be an alternative approach. If you really needed a hardened item, you could use silver steel for the pins, turn slightly over, harden, temper and then lap to final size. Sure, if you had to do 50 heads, all the same, a guide pin that is not going to wear out is the right way to go, but if the pin only needs to survive one head and then the next head, in a year's time, needs a different size anyway, other approaches might be more suitable.

That’s a valid point on how many I need to make. I want to get within a few micron of size to ensure good fit in valve guide but then most engine stuff under them reaming guides with a drill chuck and measuring with callipers so I am probably over thinking tolerances.

I will be using surface grinder as the spindle is good on that.

I see there are commercial powered centre grinding units designed to hang off
Surface grinder that work well.

You may be right about lathe getting it close then harden and finish as it will be one pin then not for a while until a different head comes along. You can buy them but I’m a stubborn old git who likes to make stuff.

Food for thought, I will look at my options.

I appreciate the replies helping me work this out

 

[pressbrake1]

Lathe then lap

 

[pressbrake1]

Bare in mind the guides are reamed finish so all this micron talk is a bit off

 

[Colin H]

Lathe then lap

Thanks Clive, sounds good to me. Thanks for advice and saving my wallet so I can spend that on a mini wheel in future.

 

[Brad93]

Mr renzetti has a good video on a split aluminium lap used on the lathe