Brown & Sharpe 2L surface grinder - drive gear teeth pitch?

I wonder if anyone could tell me the teeth pitch of the table drive gear/table rack - the machine is old and been abused such that there are teeth missing on both the rack and the drive gear , and I am wondering about replacing both . I don't imagine parts will be available off a shelf for this WW11 machine so getting new cut would be the only way... Unless I could retrofit similar parts for a modern surface grinder 

Edited By Adam Harris on 20/09/2019 16:59:53

I can't help you with sizes or pitch but take a look at some of the standard gear suppliers. I use HPC and Duval to name just two.

If you browse their sites you can most likely use standard off the shelf parts with a little bit of adaption work. Some of the bearing suppliers also hold some gear and rack supplies, try Simply Bearings.

The rack has a clump of 4 teeth missing and the gear has 3 teeth missing each separated by 5 good teeth - it looks to me that over a period of time the gear has been jumping the rack gap as the table shuttles back and forth at speed, and slamming into the good tooth at the end of the gap until another gear tooth gets knocked off. Ie. can only get worse.

As a temporary measure you could perhaps move the rack along a bit if you are only using it for small items. Since both are damaged both need replacing so you could go with anything and nowadays a metric pair is probably cheaper.

As for identifying the pitch as you have the item you are better placed than us to identify it. Place a rule along the rack and measure the number of teeth in one inch, or two inches if not a whole number. Once you have the pitch you can calculate the DP or Module for a replacement of the same general size as you won't have to go for an exact replacement when both are being changed.

Ok, doing the Pete Rimmer method (setting calipers to 3.142 inches and if an exact number of teeth then counting the number of teeth) I see that the rack pitch is DP10. Should I assume PA of 20 on the basis that Hardinge USA prefer PA20 to PA14? Actually it makes no difference as long as they both have the same PA....

Edited By Adam Harris on 20/09/2019 17:29:43

Do you think I can get away with just replacing the rack? In which case, I would like to know the PA or how to measure it...

Edited By Adam Harris on 20/09/2019 17:50:11

If you are handy with a file, a few grub screws fitted in those tooth spaces could be profiled to run. A standard gear repair method for some of us - as long as they are not high speed.

Diameter in inches divided into the (number of teeth +2) will provide the DP of that gear.

If you could put up with less travel you could scavenge a group of 4 teeth from the end of the rack and graft them in to replace the broken ones.

Filling the gap with braze and recutting the teeth is another option for a repair.

But, as Bazyle , changing both for new gives you the option to go for a more modern set.

**LINK**

**LINK**

What more could you ask for?

Thanks Brian, that looks like just the way to go. I'd obviously like to do things as cheap as possible but while repairing is cheaper and probably easier (when taking modification-to-fit into account) , I think the rapid oscillation to and fro of the table might be a bit too violent for braze recuts or imperfect forms of grub screw recuts. I did read somewhere of special nickel/silicon weld rods being very good for cast iron repairs but not sure about that and actually not sure what type of iron/steel my rack and gears are made of...

Would EN8 be fit for purpose for the rack and gear?

See the first link in Brian's post above. That's exactly the material the commercial offering would be made from.

As you have a rack, you should be able to determine the PA with a protractor. I'm in a similar position to yourself in that I have an Eagle surface grinder that I'm putting back together. In my case, the rack and gear are just worn, but there are enough good teeth on the end of the rack to determine it's MOD 2 with a 14 deg PA.

Unless very specialised heat treatments are carried out welding CI invariably leads to the formation of brittle carbides at the edges of the welded area. CI repairs should be done with nothing hotter than brazing techniques. See **LINK** and part 2.

Edited By Brian Oldford on 20/09/2019 21:21:22

Even better would be to file a piece of sheet material to be a snug fit in the tooth gap. Then measure the included angle. The difference between 29 degrees and 40 degrees should be clear.

Andrew

Edited By Andrew Johnston on 20/09/2019 22:41:58

Well Rob/Andrew,  I have a set of Axminster Ultimate Edge profile plates which cover 15, 20 , 30, 40 and other degrees, and since I am measuring the angle of the top half of the tooth side relative to perpendicular, I can assure everyone that it is nigh on impossible to tell the difference because the sizes are so small, even with my reading glasses on and a strong light! A fine enterprise in theory perhaps, but totally impractical. Maybe because the teeth are 70 years old and the profiles are somewhat rounded by use?

Edited By Adam Harris on 20/09/2019 22:24:48

Edited By Adam Harris on 20/09/2019 22:25:38

Edited By Adam Harris on 20/09/2019 22:25:51

Edited By Adam Harris on 20/09/2019 22:29:39

That's why I suggested filing a plate to fit and measuring that. Alternatively do the calculations for the width of the top of the tooth for 14.5 and 20 degres pressure angles. The difference is around 45 thou, that should be easy to see.

It won't be any time soon, but I could lift the table on my B&S No.2 and have a look at the rack in due course.

Andrew

Andrew these teeth are too worn to measure top widths accurately! Please don't bother lifting that table unless it is part of a general cleanup programme - it is VERY heavy and needs an engine hoist. I have a separate question for you , which is the positions of the Start Lever. If I position the Start lever at 3 o,clock table feed is entirely manual in both directions, and if I knock it out with the Stop Lever on the far right, it slips to 5 o'clock and becomes auto feed - This is entirely wrong isn't it? The manual says the Stop Lever knocks out the Start Lever from Auto Feed, but with mine doing Auto Feed at 5 o.'clock the Stop Lever movement does not affect it. Could you tell me how many positions of the clock - to -function does your Start Lever have? Adam

Edited By Adam Harris on 20/09/2019 22:59:42

The pressure angle doesn't matter one jot if you're replacing the rack and the gear.

If the rack is only broken in the one spot and the budget was tight I would cut that rack right at the broken part then grind the two ends so that they ended right in the bottom of the tooth valley, then flip two two halves round so they meet in the middle. Pin and bolt the two bits in place and buy or make a new gear. if the travel is lumpy over the join then shim or grind it to suit.

I'd offer to cut the gear for you but I can't do 10DP on my hobber.

Now that is a real engineer's mind at work Pete! Very elegant solution - perfect! Saves me money and I get a chance to haul out the old Rapidor nodding donkey that hasn't seen action in over 10 years! Many thanks