# Tapered Gibs



## tekfab (Jul 13, 2013)

Are there any advantages using a tapered gib set up over a parallel gib set up ? 

Mike Young


----------



## DMS (Jul 13, 2013)

I'm sure Richard will have more to add, but here is what I know.

Tapered gibs bear against both surfaces over their full length because of the way they adjust. this means even pressure over the length of the slide. They are also easier to adjust because you typically have a single adjusting screw (and a stop screw). With parallel gibs they are typically adjusted (is there any other way to adjust this type, I have never seen one...) by using set screws to apply pressure to the gib strip. This creates pressure points where the screws contact. You tend to get uneven wear, and the gib strip doesn't bear evenly.

Parallel gibs do work, I had them on my first lathe, and first mill. Both my current machines have tapered gibs, and I think it's definitely an improvement in design.


----------



## tekfab (Jul 13, 2013)

What i can't get my head around is how putting something tapered into something parallel works, of course i'm assuming the dovetails are machined parallel ? haven't checked that yet !
I'm hoping someone can give me an idiot slap. It's not the end of the world but before i try to measure/adjust it i'd like to know how/what i'm trying to achieve.  :whiteflag:

Mike Young


----------



## stevecmo (Jul 13, 2013)

Mike,

The dovetails are tapered to match the tapered gib.  You were thinking correctly.

Steve


----------



## DMS (Jul 14, 2013)

Here is a video on scraping in a tapered gib.

[video=youtube_share;LUEQhgGazAo]http://youtu.be/LUEQhgGazAo[/video]

If you pause the video at about 2:26, you can see he has the two parts of the slide layed out nicely so that you can see the sliding part is parallel, and the fixed part (the one containing the gib) is clearly tapered on one side.


----------



## Richard King (Jul 14, 2013)

I wanted to let the other guys speak on this one and DMS has done a fine job.  Tapered gibs are the best way to go as described by the guys.  The majority of machine builders put the Tap gib on the shorter side of the way system and they are stationary as you see on Bridgeport mills, they ride against the longer ways that are scraped parallel to one another,  The back of the gib is tapered and it goes against a tapered side of the short part. A small minority of machine builders put the tapered gibs on the long side of the way system.  Others may have 2 tapered gibs that are opposing each other on the short side of the ways.  This can get complicated trying to explain with-out pictures, but the bottom line is tapered gibs are the best way to go.  
I find the cheaper or not as accurate machines use the the flat gibs with set screws.
Rich

PS:  Thanks Seana for those great pic's and discription


----------



## DMS (Jul 14, 2013)

You're not kidding, those things are MASSIVE!.


----------



## tekfab (Jul 14, 2013)

Thank you all for your help and information. What i can't decide is how easy it will be to measure up and scrape compared to a parallel set up ? Both the top slide and cross slide have the tapered gib set up although it's the cross slide that i would like to "fix" first but as its a 1932 machine i'm sure another bit of time won't harm it ! I have limited experience of doing a cross slide but it was a parallel gib type and didn't need much attention.

Mike Young


----------



## Richard King (Jul 14, 2013)

tekfab said:


> Thank you all for your help and information. What i can't decide is how easy it will be to measure up and scrape compared to a parallel set up ? Both the top slide and cross slide have the tapered gib set up although it's the cross slide that i would like to "fix" first but as its a 1932 machine i'm sure another bit of time won't harm it ! I have limited experience of doing a cross slide but it was a parallel gib type and didn't need much attention.
> 
> Mike Young



Take some pictures and add them here please.   Or if you search YouTube  you will see how that same guy does the other 1/2.
Myabe DMS has it, I watched in once,  so its there.   Rich


----------



## DMS (Jul 14, 2013)

Here is the part of the video with the actual scraping. The previous one I linked just did a dry run through fitup.

[video=youtube_share;esAqz6bCVyQ]http://youtu.be/esAqz6bCVyQ[/video]

If the machine is already a tapered gib machine, you will want to stick with that. Keep in mind, I'm just a neophyte, I have only done parallel gibs as well, and most of my experience is "self taught". That being said, Nicks videos don't make it look any harder than a parallel gib.


----------



## Richard King (Jul 15, 2013)

The way I scrape the gib is different then Nick.  First thing I do is file the ends as they usually have a burr or raised from when the the gib bolt is over tightened. Then I check the gib to see if it is flat by laying the back unworn side on a surface plate, they are usually high in the middle because it wears on the other side.  I measure it with a feeler gage  It's the same thing when you mill or grind a thin piece of steel on one side it bends. After I discover how much it's bent I flatten the gib in a few different ways, I hope Tadd or Bill one of the other students who took a class can supply a picture here as I don't have one.  

But I bend it by normally by laying the gib back side up on 2 wood blocks on the ends and press down with my hand or use a c-clamp taking a small amount at a time.  I sometimes will set a mag base behind it and put a 1" travel plunger indicator on the gib and tight the clamp then loosen it until It's straight.  You will be surprised as to how much you can bend the gib and it won't break.  In the classes I shown how I can bend a Bridgeport gib a 1/4" just to show how they don't break.  

With that said on some of these small Chinese machines be careful bending them as some of the iron is very brittle.  Then I blue up the back of the gib and scrape it so it has 2 - 5 PPI and 60% coverage POP.  One thing you have to do is to check the surface the back side of the gib rests on.  That surface is sometimes high in the middle and the ends have burrs.  This should also be tested with a blued straight edge and be sure it is flat by checking the airy points or 30% hinge from both ends. Be sure to pull the gib up off the bottom of the dovetail or the hinge will look like it's on the ends.    

I don't hammer in the gib like Nick does, I put the gib in and slide the side back and forth and check the taper so both ends are the same using a mag base in indicator as seen in the picture below.  Tou have to have some slop in the test, say .003"  on the tight end. So if you push pull the part on the one end and you get .004" and move the indicator to the other and and do the push pull and you get .006" the gibs taper is off .002" and needs to be stepped scraped.  When it gets close I being finished I put the gib screws in to hold it.   I seldom buy a new gib because it slides in to far as the gibs you buy will have to be scraped.  

I just saw where a company I do work for (now) bought some new gibs for a centerless grinder because the old gibs were out of adjustment expecting them to fit.  The taper was off .015" and the work head wiggled and the machine crashed.  So don't assume the new gib will work.  My cure for a worn gib is to glue on a Phenolic shim on the back side or glue on Rulon on the front side and scrape it.  Scrape it and when I am done I relieve the middle 40% of the gib approx .0005 low", so when the gib wears it wears flatter.
	

		
			
		

		
	





	

		
			
		

		
	
    Using the Rulon makes the slide tighter and it slides like butter.  I would say 90% of all machine built today has either Rulon, Turcite, some other brand of Teflon / bronze filled wear strip on them.  I have no clue of the percentage machines coming out of China with it.  From the hand full of ones I have seen they are cast iron and in rough shape.
I need to scoot, working on a grinder this week   More later.  If any one else can add to this please join it.  Rich


----------



## Erik Brewster (Jul 15, 2013)

Richard King said:


> After I discover how much it's bent I flatten the gib in a few different ways



One thing I learned as a new scraper: Take the extra few minutes to (re)bend the gib as straight as you can. Often gibs are small and can be scraped quickly and easily. I fell for this and scraped too much material off a gib (to compensate for 0.01" or so of bend) and now it sits very deep. If I had spent a few more minutes straightening it, I would have had to scrape much less. The few minutes scraping wasn't a big deal, but the resulting fit of the gib would have been better. Remember that a bend shows on both sides of the gib, so you scrape off twice as much material as indicated by the bend measurement...

I straighten gibs on an arbor press with a magnetic attached dial indicator keeping track of how the bending is progressing. It works well, though anything will do, so long as you can measure your work and control the amount of bend you put it.

I'm really amazed at how much I took away from Rich's class. It really got me to the point where I can scrape well enough to be confident I will make the machine better, and not worse. I can't say that about many classes...


----------



## Richard King (Jul 15, 2013)

Senna said:


> Here are some pics of the tapered longitudinal gibs on my Gorton 9J.
> 
> The saddle on these 9J's are very wide (42" with a 48" table) and support the long table very well. Much longer than those on a Bridgeport for instance. Even these long supports don't entirely prevent table sag on the ends as evidenced by the worn away scraping on the ends. This table sag can be much worse on machines with a shorter saddle.
> 
> ...



It says my message is to short so I am adding this down here.  The bulk of what I said is above the 1st picture.   Rich


----------

