Figured Out the Table Binding, Now a Grease Recommendation?

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toddalin
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Figured Out the Table Binding, Now a Grease Recommendation?

Post by toddalin » Thu Mar 17, 2016 6:38 pm

Ever since the power feed snapped the spline shaft and the table locked up, I've been getting a binding in the Y-axis making lousy circles and making the table harder to use than it should be. I had to remove the table at the time and didn't shim it (verticle) and thought this could be the problem. After taking it off again and putting in a shim, a couple weeks ago, it was still too tight.

Today I was milling a piece of aluminum and the Y-axis hand wheel "came away" from the table. I could turn the wheel, but the table didn't move. But I could pull the table along while cranking the wheel to move it.

When I removed the table, I could see that the the brass bushings had pulled out from their assembly.

OK, best as what I can tell, this is what happened. The table is pulled along by a rectangular piece of metal and they are held together with four Allen screws. The rectangular piece has "barrel" atached to it and TWO threaded brass bushings that ride on the lead screw fit into the barrel, cinched tight with a couple Allen screws.

I think when the table locked up under the power feed, the two brass collars came together and acted like a lock nut, impeeding the movement along the lead screw. When I last put in the shim, I loosened the two cinch screws and didn't get them as tight and this allowed them to pull out of the barrel today. Had this of not happened, I probably wouldn't have figured out that the the two brass bushings had probably come together and were creating the binding.

This time when I reassembled the bushings/barrel assembly, I left 0.018" (feeler guage) between the two bushings and when things tightened up, I could put a feeler gauge in through the cinch area and there was still a tight 0.009" between the bushings. It feels freer. :mrgreen:

So, what is a good grease to use when reassembling the table (ShopMaster TriPower 3-in-1) and were can I get it? I'm talking a small quantity.


Edit:

Did some research and am expecting someone to say Vactra #2 from Enco. So, anyone have a current Enco discount code?

Thanks

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Gary Armitstead
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by Gary Armitstead » Thu Mar 17, 2016 8:21 pm

Edit:

Did some research and am expecting someone to say Vactra #2 from Enco. So, anyone have a current Enco discount code?

Thanks
Todd,

You know that Vactra #2 is an oil, not a grease........correct? We used to use Vactra #2 in Cincinnati Hydrotels as way lube. I have a gallon of it here. How much do you need? We can find a way of getting it to you. Like bring a clean jar up to LALS and I'll meet you there. Just say the word. :) I'll give you a 50 cent tour while you are there.
Gary Armitstead
Burbank, CA
Member LALS since 1980
Member Goleta Valley Railroad Club 1980-1993

toddalin
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by toddalin » Thu Mar 17, 2016 8:46 pm

I do now. I couldn't find it listed under grease on the Enco site, but there is was listed under oil. But if you search their site for "Vactra," nothing comes up. Ridiculous!

I ordered a gal from Enco. It just happens that today, of all days, EVERYTHING is 25% off with the code GREEN. Was ~$24 with shipping. I could have got a quart on ebay for ~$20 with shipping, but Enco is the better deal.

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ctwo
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by ctwo » Thu Mar 17, 2016 9:03 pm

Really? 25% off?
Standards are so important that everyone must have their own...
To measure is to know - Lord Kelvin
Disclaimer: I'm just a guy with a few machines...

toddalin
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by toddalin » Fri Mar 18, 2016 1:53 pm

ctwo wrote:Really? 25% off?

Yes, everything. Hope you cashed in quick 'cause today's another day.

They even took 25% off the Internet sale price that was marked down from $24 to $18.

:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

You have Applied the following promotions:
GREEN - Save 25% on all orders

Packing
Slip No. Status Invoice
Date Invoice
Number Ship
Date Tracking Info Total
Price
5695783 IN PROCESS Not Available $13.50
Model No. Description Qty. Price Tax Ext. Price
505-1987 VACTRA #2 1 GALLON MOBIL WAY OIL 1 $13.50 $13.50
Sub Total $13.50

TomB
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by TomB » Fri Mar 18, 2016 3:09 pm

There is more to the two brass bushings and the square block than you are recognizing. You will find the bushings are very loose threads on the Y-axis drive thread and if not put in correctly they will lead to backlash in the Y-axis. On my machine the two bushings are separated by a light spring that pushes them apart. Compared to the forces on the drive the spring force is nothing but when just the screw, bushings and spring are considered the spring force is sufficient that the two bushing threads seat on opposite sides of their threads. Given that condition, if you can get the hole in the square block open enough that the bushings will side through the hole without compressing the spring you can then tighten the block to lock the bushing into the table while the drive ends of the bushing threads remain in contact with the tread shaft on opposite flanks.

Why that effects backlash is hard to describe but here goes. To keep the sentence shorter call the drive shaft and two bushings 'S', 'F' and 'B' (for front and back) and call the sides of the shaft and bushing thread's 'f' and 'b' similarly. With the bushing spread by the spring then the contact surfaces will be Sb-Ff and Bb-Sf. I think the drive shaft is a right hand thread so imagine the crank turned CW to push the Sb-Ff contact tighter and move the table back. Then imagine changing the rotation direction to CCW. The working contact surface would immediately switch to Bb-Sf and the table would be pushed toward the front. Normal backlash is eliminated because the bushing thread does not shift back and forth across the thread gap.

Based on my experience I would not think the two anti-backlash bushing have anything to do with binding. My machine is right now back in NY because I have not moved it yet and apart because the Y-axis binds. I have a bind that is periodic and tied to the the crank rotation position. As I turn the crank the table binds at 4 o'clock then releases goes around nicely until it binds at 4 o'clock again. The problem is a bent Y-axis drive shaft which I was starting to straighten just before I had to move to VT. A crash had bent it but when I took things apart and measured everything I found that the shaft had bent instead of the bushing being pulled out. I believe that was because the entire geometry of the assembly was screwed up. When the machine was put together the back end of the shaft apparently would not fit into the back support bushing (not one of the anti-backlash bushings) so the assemblers just reamed it egg shaped. If the table was to the back the drive shaft was pulled up about .1 inch and if the table was to the front the drive shaft was pulled down .1 inch. When the crash occurred the drive shaft twisted slightly and then slammed the end into end of the back support oval to impact bent it. The resulting 'twisted and bent' distortion is small but enough to produce the binding. I would suggest you look carefully at the potential of bends before jumping to worrying about the anti-backlash bushings.

Hope this is helpful
Tom

toddalin
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by toddalin » Fri Mar 18, 2016 4:26 pm

Thanks Tom,

I understand what you are saying. My machine doesn't have the spring betwen the bushings and I can easily push them though the barrel when it is loosened.

I'm thinking that if I turn the front and back bushing, front and rear a bit, respectively, that would set them to remove the play in that direction, respectively. Then I can slide the barrel over the bushings and cinch it down.

TomB
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by TomB » Tue Mar 22, 2016 2:45 pm

I believe you could mount the bushing to take up the slack with a different procedure that might or might not be easier. Suppose put both bushing into the square block while on the drive thread,and then tightened the front holding screw in place. Then hold the table back while cranking the table forward, hand pressure is probably enough. That would force the back bushing as far back from the front bushing as the thread permits.While its in that position tighten the back holding screw. To make it reachable I'd assemble the table with the bushings and block toward the back of the travel then I would remove the back of the table carrier so I could reach the tightening screws. If yours is a sold square block that still might not work. I did not thinking clamping the two bushings with one bar was a good idea so I sawed my square block about in the middle and slightly more than half through. That way each of the clamping screws apply pressure to only one bushing.

toddalin
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Re: Figured Out the Table Binding, Now a Grease Recommendati

Post by toddalin » Wed Mar 23, 2016 12:17 pm

Actually, with mine, you can put the two bushings into the block and there is a slot in the block right between them. Also, the two bushings form a "V" where they come together.

So when you press a feeler gauge or bevel into the slot, as I did, it wants to go between them forcing them outwards on the thread while you cinch it down.

May have been one of ShopMaster's better ideas.

Edit, I did have some slop and redid it.

I set the rear bushing and tightened it then inserted a feeler gauge and could pry the front bushing away and tighten its set screw. This does take out the slop, but also makes it a bit tighter to turn.

I've also gone over the ways both on the table and chassis, and jib with steel wool and carb cleaner and they are smoother. I'll probably clean the lead screw with some brake cleaner (carb cleaner would remove the paint), before oiling (Vectra #2) and putting it all back together.

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