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Bridgeport 815 surface grinder/ walker cermax permanent magnetic chuck question

wagsha48

Aluminum
Joined
Nov 23, 2016
Over the weekend I bought this Bridgeport 815 surface grinder for $250 and much to my surprise it appears to be nearly operable! Just have a few questions for anyone familiar with these machines or walker chucks.

The spindle: it has a 1.5" hub and looks to be a 3" TPF taper. Looks like it shouldn't be too hard to track down a 1.25 hub so I can use standard wheels. The hub has no nut, wouldn't be much work to make one but I really would rather have a 1.25 anyway. Is there any reason I shouldn't change it?

The chuck:Wouldn't hold at all. looked good on the outside but it had been infiltrated with water at some point and the metal strips underneath the magnet were in pretty bad shape. I replaced the two long ones which had corroded in half, the rest were intact so I left them alone. What is the purpose of these strips? They are about .010 thick, my replacements were .015 but it didn't look like the difference would matter. The magnet seemed a lot stronger with the new strips.

Also the springs weren't looking too good. They were partially corroded away but still looked strong enough to hold up the magnet when it's in the off position. Doesn't seem critical to me since when it's on the magnet is connected quite solidly to the top plate.

My main concern is the cam-link that actuates the magnet. The side that is connected the the handle had a slot rather than a hole. Not sure if that's how it is made or if it wore like that. My theory is that the magnet, being rather powerful, will probably find the sweet spot on its own given the freedom provided by slot slot. If I am wrong please inform me so I can make a new one.

When it was all cleaned and lubed it had holding power almost equal to the unabused chucks on the grinders where I work. I vehemently disagree with those who advise against servicing mag chucks. Mine work out fairly well all things considered. Just looking for a little advise in regard to my findings so I can proceed to optimize the chuck.

Also it's a 3 phase grinder. I use a fancy new Teco VFD on my Bridgeport, but I am figuring a solid state phase converter should be fine for this considering I won't be using it for extended periods.

I apologize for my lack of pictures of the inside of the chuck. I was pretty proud of my work and wish I would have thought to snap some photos! Next time. IMG_1064.jpg
 
Also it's a 3 phase grinder. I use a fancy new Teco VFD on my Bridgeport, but I am figuring a solid state phase converter should be fine for this considering I won't be using it for extended periods.

I think a Teco VFD would be fine even for extended 24x7 operation!
 
I have the same grinder. 1.25" hubs will work fine, and will allow you to use 7" wheels. Go for the VFD. It will allow you to speed up those smaller wheels to work correctly and to tailor the speed to the job. Plus it will start the spindle gently and not knock the wheel out of true after being dressed.
 
I suppose since my grinder and my mill are pretty close in specs I could rig up a junction box and use the old reversing switch off the BP to select either the mill or grinder, shouldn't need both at once but then again it's might be nice to have the option to keep the spindle turning. I'm sure as heck not buying another new TECO 7300 CV! Its a great drive but very expensive. Worth it to fine tune my mill RPMs though. It is awesome at compensating for spindle loads at low RPM, saves a lot of belt changing/breaking tools because I was too lazy to change the belts. Anyhow I don't necessarily need those capabilities on my grinder. Soft start would be nice though.

Any suggestions on the merits of the transfer switch vs a separate VFD? I'd probably go with a used TECO or something like that over a new huanyang. Can't stand them
 
Replace the link, theholes for the pins are round when new. Walker sells a kit with the link and a bushing for the pivot arm.

In use the link cams the magnet a small amount off the top plate when flipping the lever, with worn holes the magnet never moves all way to cover 2 poles, that is why the holding is low.
 
To those of you that have a Bridgeport 8 x 15" surface grinder. How are they working out for you? The reason I ask is back in the late 70's when I was an apprentice the shop I worked in bought one new when they first came out. After a few months the table and saddle got very hard to turn. Removing the table revealed that the scraping was so shallow that it quickly wore down and the table tried to ring to the saddle. (Yes we oiled it regularly) I was wondering if that was a typical problem with these Bridgeport surface grinders.
 
To those of you that have a Bridgeport 8 x 15" surface grinder. How are they working out for you? The reason I ask is back in the late 70's when I was an apprentice the shop I worked in bought one new when they first came out. After a few months the table and saddle got very hard to turn. Removing the table revealed that the scraping was so shallow that it quickly wore down and the table tried to ring to the saddle. (Yes we oiled it regularly) I was wondering if that was a typical problem with these Bridgeport surface grinders.

Mine's still almost new, not enough use to wear in yet.
 
I have the same grinder. 1.25" hubs will work fine, and will allow you to use 7" wheels. Go for the VFD. It will allow you to speed up those smaller wheels to work correctly and to tailor the speed to the job. Plus it will start the spindle gently and not knock the wheel out of true after being dressed.

Use of 1 1/4 wheels allows much lower price as many 7" can be bought used or new at auction.. doing a lot of grinding and it is good to keep certain angles, radius and width wheels ready to skim dress and get back to grinding. I like to keep wheels on a 1" wood peg wall board with having a cover to keep room dirt and oils off the wheels. Clear cover so yoo can see the wheels.
 
Mine seems to have been used a reasonable amount and the table still moves fairly well. I'll examine the scraping next time I lift the table. I would really like to run 7 1/4 wheels but it's a 1750 rpm spindle. Anybody have any experience trying to get a decent finish with such a low sfm? I just ordered a 10" wheel pretty cheap but a 12" wheel is pretty pricey and hard to find less than 1" thick. I might consider a spindle transplant if I can find one
 
WRT wheel arbors, Sopko is your friend.

As far as the spindle goes, I take it that it's a direct drive, if it's belt drive, you may have options, ask Sopko if the bearings can handle the speed.
 
I ended up using the old reversing switch from my mill to switch my vfd between milling and grinding so I can increase the frequency for 7" wheels, a 10" wheel does ok at 1750 but I'd rather not buy a 10" diamond wheel for when I grind carbide. Kind of a PITA to have to go into the VFD settings every time I grind but it beats the price of a new inverter. And yes the BP 815 is direct drive so not many other options but it seems like a decent machine. My Walker chuck ended up not working out too good, still cant get much pull. I tried several different cam geometries for the throw and only saw negligible gains. Now im downgraded to my B&S 5x10 which is about 10x stronger but I haven't lost hope in the walker just yet
 








 
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