Surface Grinder Cross-feed Nut

[thestelster]

Well, doing a small job this morning with my Brown & Sharpe 612 Micromaster, and the crossfeed handle is sticking, and then getting harder to turn, and then free wheeling and no movement of the table@#$%!

Looks like the bronze crossfeed nut is stripped.

Unlike many surface grinders, the B&S table the z-axis is fixed. The whole spindle, motor, housing, moves. That's a lot of weight that the crossfeed screw has to overcome.

I'll have to get on this soon.

What a pain in the....!!

 

[140mower]

That sucks, but at least it happened to our threading guru.....
One more segment to the threading series I suppose? .....

 

[thestelster]

That sucks, but at least it happened to our threading guru.....
One more segment to the threading series I suppose? .....

Haha!! Yeah, I suppose!

 

[Susquatch]

Unlike many surface grinders, the B&S table the z-axis is fixed. The whole spindle, motor, housing, moves. That's a lot of weight that the crossfeed screw has to overcome.

Ouch!

Not clear to me which axis is which Stel.

Your grinder looks similar to mine.

Forgetting about what is really X Y & Z, mine has the table riding both ways separately. The Lengthwise (right and left) sits on top of the in and out axis. So the in out carries more weight than the right left. Good thing too cuz the right left is where all the action is.

My spindle goes up and down separately. So the spindle height screw only carries the spindle and motor weight. Not the table.

 

[thestelster]

Ouch!

Not clear to me which axis is which Stel.

Your grinder looks similar to mine.

Forgetting about what is really X Y & Z, mine has the table riding both ways separately. The Lengthwise (right and left) sits on top of the in and out axis. So the in out carries more weight than the right left. Good thing too cuz the right left is where all the action is.

My spindle goes up and down separately. So the spindle height screw only carries the spindle and motor weight. Not the table.

My table only goes left right. The tower that houses the spindle and motor moves forward and back.

 

[thestelster]

Well, I took the crossfeed screw and nut out. What a pain! The rear end bearing housing was right over the tower so I couldnt get at the bolts, of course the tower doesn't move since the nut is stripped, so I had to improvise with a ratcheting tie-down to pull the tower forward.

 

[thestelster]

Once the rear bearing was released from the cross-slide screw, there was just enough bite that I was able to unscrew it out the front.

Then I had to reach in contorting body and hands to uncrew the 4 bolts holding holding the crossfeed nut housing in place.

Anyway, eventually pressed the bronze bushing out.

2 part bushing to remove all play. The screw threads look pretty good, although it's been repaired before by splicing the acme threaded section into the non-threaded section.

7/8"-10 Acme - RH

 

[thestelster]

Looking a the parts schematic for several of the B&S surface grinders, and some on-line photos, the cross feed nut is one piece.

Since I will be making this nut myself, single point threading, is there any reason why I shouldn't. Looking at the nut I removed, it looks as though it use to be one piece, and then they parted into two pieces.

Perhaps the nut was worn, and instead of making a new nut, they cut the piece in half, and incorporated pin spanner holes on the one end to remove the backlash. They also used split pins to secure the two parts to the housing.

And the oil ports on the housing align up with those on the nut.

 

[thestelster]

I sent an email to Bourn-Koch, the supplier fo B&S parts.

The leadscrew is in stock @ $3,000.00 cdn, and the nut is in stock too @ $1,700.00 cdn!

At least they sent me the parts schematic for that section of the surface grinder. And according to the schematic, the nut is a single unit.

Well, I have the bronze to make a new nut, I just have to order the acme thead insert.

 

[140mower]

I sent an email to Bourn-Koch, the supplier fo B&S parts.

The leadscrew is in stock @ $3,000.00 cdn, and the nut is in stock too @ $1,700.00 cdn!

At least they sent me the parts schematic for that section of the surface grinder. And according to the schematic, the nut is a single unit.

Well, I have the bronze to make a new nut, I just have to order the acme thead insert.

..... So, for about a $100. worth of bronze they zing you $1700....... I want to work there, for that kind of money even the janitor should be making 6 figures....

 

[thestelster]

..... So, for about a $100. worth of bronze they zing you $1700....... I want to work there, for that kind of money even the janitor should be making 6 figures....

I was thinking the same thing.

And the question is....who in their right mind would pay that? I would think that anyone who has a surface grinder would also have a lathe that would be able to make their own part.

The most time consuming part of the job was getting that part out of the surface grinder!!

 

[RobinHood]

The leadscrew is in stock @ $3,000.00 cdn, and the nut is in stock too @ $1,700.00 cdn!

I’m in the wrong business. Maybe a retirement opportunity?

 

[Susquatch]

Well, I have the bronze to make a new nut, I just have to order the acme thead insert.

Hard to believe you like inserts that much........

For just one nut, I'd be grinding my own hss tool and already be using the surface grinder......

 

[thestelster]

Hard to believe you like inserts that much........

For just one nut, I'd be grinding my own hss tool and already be using the surface grinder......

Well, the nut is 3.5" long with a bore of 0.775". Haha, you might still be grinding that hss tool by the time I get the insert

 

[Susquatch]

Well, the nut is 3.5" long with a bore of 0.775". Haha, you might still be grinding that hss tool by the time I get the insert

Ya, 3.5" is a long nut for sure! But even on an insert style boring bar, that's a deep hole for a 5/8 or 1/2" bar.....

Sometimes I like to use preground hss and just modify it for my needs. But I don't have anything longer than for a 2" depth. So ya, I'd still be grinding...... LOL!

 

[thestelster]

I have a 5/8" Sandvik threading bar, which isn't an ideal L/D, I wish it was carbide, but at over $800, I don't think so.

So we'll have to make do.

I was also thinking of buying another steel threading bar, cutting off its head and brazing it to a carbide shank. But a 12" x5/8" carbide bar is over $300.00.

 

[RobinHood]

I have a 5/8" Sandvik threading bar, which isn't an ideal L/D, I wish it was carbide, but at over $800, I don't think so.

Look on the bright side: that would still be $800+ cheaper than the nut off the shelf…

 

[thestelster]

Ok, I started making the new nut.

-7/8"-10 acme -Right hand.
-95400 aluminium bronze
-10 tpi acme full profile un-coated insert
-Sandvik 5/8" internal threading bar

1. Turned OD to 1.376"
2. Drilled and bored to 0.775" (minor diameter)
3. Bored a thread relief at the deep end, 2.5" using an 8tpi UN insert (I need to get internal grooving inserts on of these days.)
4. Proceeded to thread until reaching required depth and tested by screwing in lead screw. Won't go in.
5. Take off a couple thou'. Starts to thread but..no
6. Took off a couple more thou'...not yet.

Because this is a full profile, it will form the appropriate thread shape and start to top off.

7. Now the minor diameter is opened up to max (0.780"). And still doesn't go in. WTF is going on?

 

[Bandit]

I thought it was acme thread, but the picture of the new nut does't really look acme. A tricky picture? The same with the insert. I can see the topping part of the insert, but the there does not appear to be a bottoming part for an acme thread, looks like for a regular thread. Another tricky picture? Or?

 

[thestelster]

Ok. Something is not right. Lets have a look at the crossfeed screw. I mentioned previously that it was repaired. They lopped off the old threaded section, made a new piece and attached it to the rest of the crossfeed screw.

Lets measure the pitch diameter. Calculated to 0.865"
It's supposed to be 0.825".#$%@#^&!!!

Let's take a close look at the thread. Shut the front door.....it doesn't look to be an acme angle of 29°