Making a tapered gib

[T. J.]

I need to make a tapered gib for the cross slide of an Enco lathe and I could use some advice from someone who’s done this. I’ve got the basic process and work holding problems figured out (I think). My question has to do with how much extra material to allow for fitting the gib. The length of the finished gib will be 12.25”. It is .355” on the thick end and 0.213” on the thin end (0.0116” taper per inch). The dovetail angle is 60 degrees.

I’ve studied the chapter in the Connelly book where he discussed gib construction. In the example he gives, he suggests making the gib 3” longer than it’s finished length. I understand this - when scraping the gib, you’re going to be removing material and it will insert farther into the cross slide. When you’re done, you cut off the excess on each end.

This is what I don’t get. He goes on to suggest that you should add 1 - 2 times the taper per inch (0.020” in his example, 0.023” for mine) of thickness to the machined gib to allow for fitting. That’s a ton of material to remove by scraping! Why this extra safety margin? I’m inclined to make this margin much smaller (say 0.001-0.002”), but I want to make sure I’m now missing something. What do y’all think?

 

[benmychree]

Ask Rich King. But I would allow the 3" extra length with the gib starting to pass trough the small end or not quite there. The gib will undoubtedly have some bend in it after machining, so likely there will be plenty to scrape before it fits correctly.

 

[rabler]

First add three inches. Does this three inches get added to the short end or the long end? Because adding 1-2 times the taper/inch may not have to be scraped off if you just shift the gib 1-2 inches. Could this be interpreted as shooting for the excess to be on fatter side? Just trying to think it through, I’m an interested neophyte.

 

[T. J.]

Does this three inches get added to the short end or the long end?

This would be added to the thicker end

 

[matthewsx]

I needed one for the cross slide of my Samson lathe and just found one from a similar Grizzly machine. It works great, I suppose give time and tooling I could have made one myself but I was happy to shell out the $12 + shipping to have one sent to my door.

This is the one I got, I plan to scrape it at some point and may need to start with a new one but I know where to get it.

Parts for 12" x 24" Gear-Head, Cam Lock Spindle, Lathe - Grizzly Industrial

Grizzly Industrial, Inc. is a national retail and internet company providing a wide variety of high-quality woodworking and metalworking machinery, power tools, hand tools and accessories. By selling directly to end users we provide the best quality products at the best price to professionals...

www.grizzly.com

John

 

[woodchucker]

are you milling it or grinding it?
I would add the length like you say to the larger end since you are always looking to tighten it, and you can always remove but can't add.
Next, when you say add it to the taper per inch... I think he meant to the overall thickness in general, not changing the angle..

if you don't have a surface grinder, you're going to be working hard to scrape it. Do you have a magnetic sine plate?

 

[T. J.]

are you milling it or grinding it?
I would add the length like you say to the larger end since you are always looking to tighten it, and you can always remove but can't add.
Next, when you say add it to the taper per inch... I think he meant to the overall thickness in general, not changing the angle..

if you don't have a surface grinder, you're going to be working hard to scrape it. Do you have a magnetic sine plate?

I’ll be milling it - I don’t have a surface grinder. Yes, the thickness would be added over the entire length, keeping the taper angle the same. He was just using the amount of taper as a rule of thumb for how much thickness to add.

 

[ErichKeane]

So as you've figured, there are 2 ways to make sure you don't make your gib too 'thin' initially to get it prepped. The first is to make it 'thicker'. The second is to make it longer on the thicker side.

The former is 'cheaper', the latter is 'easier' to get it fine-tuned. With the former, you have to keep taking material until it fits perfectly, and if you go even a little too far, you scrap the part. Making it too long means you scrape/etc until it 'fits', then just cut off the excess.

 

[Richard King 2]

He and I spoke or wrote on my FB forum. I suggested he check the taper with 2 feeler gage sets at the same time instead of telescope gages. I also found a web-site that sell manuals. They might sell parts too. That's a great idea Matthew

 

[Janderso]

It seems to me Kieth Rucker made one for someone.
An interesting job. Pretty complex.
I would think a compound, magnetic sine and a surface grinder would be in the tool list.