Small Machine (Rusnok) Gib Questions

catalytic · Jan 23, 2017

I recently got a little Rusnok mill, and when it arrived the X-axis table gib had slid out, gotten hit by something, and bent/cracked (it appears to be case hardened steel or cast iron, and it hairline cracks around the bend). I just got a replacement from the folks at Electro-Mechano.

Gib Dimensions: 13" long X 0.34" wide X 0.103" thick (replacement gib) or 0.124" thick (original gib). It is not tapered.

The old gib was 0.124" thick, whereas the new one is 0.103" thick. Does this 0.021" difference in thickness matter?

Second, the new one has a slight bow. When I lay it down on a flat machined surface, it bows up 0.05" in the middle. It takes very little pressure to push the bow down flat. I don't think it can be permanently bent back to straight -- I tried that with the original bent gib and it cracked before it bent. Is this bow a problem, and if not, should it bow out towards the operator or in towards the column? (the gib is located on the operator's side of the table)

Third, should I do anything to the new one before sliding it in?

Pic of gibs:

Here is how I'm measuring thickness:

Pic of bow:

bmikkalson · Jan 23, 2017

Fun project. The length should not affect just means it will slide in further or less. The bow is a deal breaker. You are going to need to press it straight as possible and and check for flatness on a surface plate on the sliding bearing side. Flatness is important as it is a bearing surface. If you can't get it flat pressing . U may have to machine and scrape. Could u maybe send it back and get another one?? I mean you have 2 junk guns now.....It must have some stresses in it to be bend .
The gib is a bearing surface, like a movable dovetail.
Hopefully some smarter guy will step in, but this will get u started. Ask the guys over on the machine rebuild forum. They know!!!

dian · Jan 24, 2017

is that a tapered gib?

catalytic · Jan 24, 2017

dian said:
is that a tapered gib?

No - it's not tapered. I edited the original post to add dimensions and pics of bow.

dian · Jan 24, 2017

then dont worry if its bent. polish the bearing side.

catalytic · Jan 25, 2017

dian said:
then dont worry if its bent. polish the bearing side.

Great. Should I worry that it is thinner than the original? The original is 0.124" in the smallest dimension, whereas the replacement is 0.103". Or is it OK to take up this much using the gib adjustment screws?

Billtodd · Jan 25, 2017

Try peening it straight. A springy gib will wear faster and make it difficult to adjust properly.

Bill

L Vanice · Jan 25, 2017

I would return the bent new part, more because it is thin than because it is bent. But bent should get them to refund including shipping or send a free replacement. If they do not have an exact size replacement, I would make a new part out of annealed precision (not oversize) O-1 flat stock. A 1/8 x 3/8 x 18 inch piece is $16.83 from Starrett. There ought to be a Starrett dealer in Boston, Los Angeles or Cleveland. Part No. 57229: 1/8" Thickness x 3/8" Width x 18" Length

Flat gibs should be as thick as will fit between the mating parts. A thin gib will deform easily and only contact the sliding surface in the vicinity of the set screws.

You want as much sliding surface contact as possible. Hardinge made some of their flat gibs with the lower edge beveled and the upper edge square. Some gibs have both narrow edges beveled. A gib with both edges square leaves some of the sliding surface missing contact with the gib.

Larry

magicmaker · Jan 25, 2017

I just checked one of the gibs on on my Rusnok and thickness is .125". This is an original gib not a replacement.
Jim

dian · Jan 25, 2017

its weird the gib doesnt have dimples for the set screws. what do the tips of the screws look like? do they have a point matching the angle?

partsproduction · Jan 25, 2017

Re ask in Machine tool scraping section, a lot of wisdom in that section about gibs and how to tweak them and scrape them in. I've seen flat gibs in steel but never yet in cast iron, though I'm sure for larger machines cast iron would be preferable, OTH I've never seen a taper gib that was not cast iron, FWIW. Steel against cast iron with lubrication should last a long time. Can you do the spark test on the original to see if it is cast iron?

catalytic · Jan 26, 2017

L Vanice said:
A 1/8 x 3/8 x 18 inch piece is $16.83 from Starrett. Part No. 57229: 1/8" Thickness x 3/8" Width x 18" Length[/url]
Larry

Thank you! This is a great backup option. Based on all of the advice here, I'll give them a call in the morning and see what can be done about this one.

magicmaker said:
I just checked one of the gibs on on my Rusnok and thickness is .125". This is an original gib not a replacement.
Jim

Thank you for checking!!

dian said:
its weird the gib doesnt have dimples for the set screws. what do the tips of the screws look like? do they have a point matching the angle?

No -- they are steel set screws with flat tips. The gib is held in place by a spring pin (which goes through the hole drilled in the gib).

partsproduction said:
Re ask in Machine tool scraping section, a lot of wisdom in that section about gibs …… Can you do the spark test on the original to see if it is cast iron?

I'll ask Electro Mechano what it's made out of. Based on the fact that the original got a bunch of hairline cracks when I tried to bend it back straight, I had thought it might be case hardened or something. Probably not regular old mild steel at any rate.

dian · Jan 26, 2017

"No -- they are steel set screws with flat tips. The gib is held in place by a spring pin (which goes through the hole drilled in the gib)."

that is unusual. so the gib sits on the bottom of the slot and the runout of the screw influences tightening?

JST · Jan 26, 2017

That's just a regular "American gib", Usually mild steel, could be hardened for wear. A little surprising that it has no screw pockets, even the cheap (forbidden brands) machines tend to have pockets.

The bowing is not much, I'd put it in and use it as-is. Put it with bowed out part as the sliding surface. It will be very slightly springy when tightened, but you won't notice. It looks like maybe 3/16" bow over 13", which is nothing that will cause an issue.

As for the thickness, no difference. Just another fraction of a turn on the screws. This style of gib is not very sensitive to slight variations of material thickness.

Use it

partsproduction · Jan 26, 2017

The cracks part is strange. I've straightened cast iron gibs before, and never broke one doing it.

catalytic · Jan 27, 2017

I talked to Electro Mechano this morning. They say to install it -- it should be completely fine -- but if I measure a difference in performance then they'll send me a new one.

They confirmed that the new gib is 1045 steel, not hardened. They start with 1/8" stock and grind it down to spec, so it comes in under 1/8". I guess this particular piece needed about 0.021" of grinding. They say they've been doing it this way for at least 15 years, but they weren't sure what they were using for gibs before 1979 (which my machine predates).

Being compulsive, I may try to make a new gib out of the Starrett Precision ground O1 posted a few replies back.

Here are some pics of the original that I removed, and they show the crack pattern that occurred when I gently tried to bend it back after it slid out and got hit by something. Doesn't look like not-hardened 1045 to me:

partsproduction · Jan 27, 2017

Sounds like you would have been ahead just buying 1/8" W2 ground flat stock.
There is no advantage in a thinner than OEM gib, and taken to extremes such a thin gib will fail early and/or damage the ways as the setscrews force dimples through the other side. You could do what many of us do when restoring machines, adopt the attitude that when possible replacement parts will be made with materials that exceed OEM materials or even tolerances when you are positive closer tolerances will not cause their own problems, which is to say going against tolerances designed to enhance longevity or reliability.

Unfortunately some engineering is designed to save pennies instead of making the machine better.

In this case you could possibly replace the gib with 1/8" blue tempered spring stock for instance. They are around 45 Rc and are machinable but polished and a good gib material against cast iron for a flat gib, but ask the experts who rebuild machines for a living, for me it's jut a hobby and how I upkeep my own machines in the shop. I do know that working on and rebuilding machine ways is a good way to remember to oil them often!

Matthew Gregory · Mar 26, 2017

Just seeing this thread. My lil' Rusnok is running pretty fine, still, but I'm sure at some point I'll need to address this, too. Did you end up using the ones Electro-Mechano sent you? How did they end up working?

I tried calling them two days ago and got a voicemail mailbox with not greeting. Didn't leave a message. I'd spoken to the owner late last year, and he was actively seeking a buyer for the company. I'm wondering if he's not out of this game, entirely, at this point...

catalytic said:
I talked to Electro Mechano this morning. They say to install it -- it should be completely fine -- but if I measure a difference in performance then they'll send me a new one.

They confirmed that the new gib is 1045 steel, not hardened. They start with 1/8" stock and grind it down to spec, so it comes in under 1/8". I guess this particular piece needed about 0.021" of grinding. They say they've been doing it this way for at least 15 years, but they weren't sure what they were using for gibs before 1979 (which my machine predates).

Being compulsive, I may try to make a new gib out of the Starrett Precision ground O1 posted a few replies back.

Here are some pics of the original that I removed, and they show the crack pattern that occurred when I gently tried to bend it back after it slid out and got hit by something. Doesn't look like not-hardened 1045 to me:

catalytic · Mar 27, 2017

^^ I talked to EM and got a parts order from them a few weeks ago. The 'business for sale' website has been there for years, but they seem to be very much still in business. I would keep trying their phone number. One of the times I called, I got a no answer/weird voicemail too, and it turned out that everyone was out on a sales trip but back a few days later. Also, EM makes several machines, and I don't think the rest of them are part of the 'business for sale' offer (don't quote me -- just based on the website I saw).

I haven't tried the gib in my machine, as the machine just got painted yesterday. It will be a few days before I reassemble everything. I do plan to use it. If it doesn't feel right, then I'll make my own replacements from ground flat 1/8" thick stock (I didn't know this was a standard stocked item anywhere until I saw the replies in this thread).

onecut · Mar 27, 2017

I would try your replacement in see if it affects your table movement.I dont think it will as your getting a replacement that undersize one is free so you could straighten it.Again dont think its necessary-you can Iv done it.Depends on your press mine has a flat table on lay it flat on bottom press move it,press,press.press move it along slightly between each press dont put any thing under it.I wouldnt even have bought one they are simple to make 10mins and its done bit of ground .125 stock I have a tipped tool set it at angle put the side angles on.Thats it done simple.

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