R8 - Wimpy or Wonderful

[Bob La Londe]

I am looking at (already have the money ready) bringing a decent new knee mill into my shop. Not a CNC. Just a work horse for doing some things quickly that are not set up easily or are impractical on a small bed mill. I like the idea of sticking with an R8 spindle for the wide array of affordable tooling available, and of course I could slap a ground face 3/4 collet in it and use any of my TTS tooling. I have been looking at maybe not the highest end, but higher end machines and they seem to be split between R8 and NT40 spindles. To be fair I have looked and there is some affordable NT40 tooling available, but I don't have any at all. I would have to start from scratch.

In the size range of machines I am looking at they are also split between 3HP spindles and 5HP spindles. Can R8 handle a 5HP load? When would you use that much power? I know that's a broad question, but the only machine i have with that much power is the Hurco with a Kwik 200 taper, and I don't think I ever put anywhere near that much load on the spindle. Hurco actually rated the machine at 4HP even though it has a 5HP motor.

In some cases the NT40 machine is cheaper than its exact compliment with the R8 spindle.

[chipmaker4130]

I don't think I'd go above 3hp for R8. Unless you're trying to run big shell mills I don't think you'd ever need more than 2! My little Millrite has a one-horse motor and I've never even slowed it down. I hog a lot with roughing mills up to 1" diameter and in general don't go easy on the machine. Never needed more power than the 1hp. Doesn't really answer your question, I guess, but I've cut a lot of steel with an R8.

[Doozer]

NMTB40 has drive tangs.
R-8 does not.
Torque drive capacity has your answer.

-Doozer

[nickel-city-fab]

If you are currently doing everything OK with R8 then I would stick with that. BUT if you see yourself maxing out the new mill with new jobs in the future, then the 40 taper maybe better. 5HP is a lotta grunt.
.
Here's my dream machine: https://www.grizzly.com/products/gri...with-dro/g0827
But first I have to win the lotto and marry Dolly Parton.

[Rich Carlstedt]

One thing you may want to consider Bob , is getting a Kwik-Switch Spindle for the knee milll. My friend had one 4 years ago that he got on eBay, but he passed on and I don't know what happened to that one , but they did have them for Bridgeports. That would really solve your problem
Rich

[JRouche]

I don't think I'd go above 3hp for R8.

Wow. You gave it some balls. I would not use it on a machine above 1.5hp (which they might have been designed for). Just for safety reasons. You dont want to spin yer spindle cause the lil key broke or the friction let go. JR

[JRouche]

I am looking at (already have the money ready) bringing a decent new knee mill into my shop.

To be fair I have looked and there is some affordable NT40 tooling available, but I don't have any at all. I would have to start from scratch.

See the thing is, you already are looking at the upgrade. Just by buying the capable machine. Well, and you have a line on some 40 holders. I know what I would do. If I had the space JR

[JRouche]

One thing you may want to consider Bob , is getting a Kwik-Switch Spindle for the knee milll. My friend had one 4 years ago that he got on eBay, but he passed on and I don't know what happened to that one , but they did have them for Bridgeports. That would really solve your problem
Rich

Again, looking in my parts drawer Rich?

I have two sets there waiting for the transplant. My BP is already wired that way. The bearing sets? Dont ask, and they have to be a set, all three. The spindles are free compared.

I like the clamping or holding that the acura-grip and acura-flex collets have. And I have too many holders. So yeah, RF-45 type with a bad assed spindle. NOT

Its too slow. The change out. Its a spanner at the nose nut if you havent seen one. JR

[Tobias-B]

The Taiwanese BP knock- off I have has a 5hp 3 phase motor on it. I've used it with some pretty big (3-4") shell mills,
and the belt (yep, standard v- belt) always starts howling before the R8 slips. Even if it's running in low speed on the
cogged belt reduction drive. Same was true of the 'mill drill' I had before that. And at that point, I had 3 phase 240 coming off the pole,
so the motors were really capable of developing rated power.

So I don't think you'll be able to GET all 5 horsepower through the primary drive pulleys. Unless you see doing a lot
of heavy work, I'd think the R8 would be fine on a knee mill. Based on a sample of the 2 machines I've used with bigger motors.

That said, I'd love to find a smaller horizontal mill for the fun factor, and to be able to do the heavier things faster.

t

[Ian B]

Given the choice, I'd take an NT40 machine any day.

For the tooling that you have, would it be possible to make an NT40 to R8 reduction sleeve? Use an R8 drawbar to hold everything in place.

Ian

[Paul Alciatore]

That's what I was thinking. Get the NT40 spindle. And get a few adopters for now.

As you find need for NT40 tooling, buy it. But use your existing R8 stuff where it will work.

Best of both worlds.

Given the choice, I'd take an NT40 machine any day.

For the tooling that you have, would it be possible to make an NT40 to R8 reduction sleeve? Use an R8 drawbar to hold everything in place.

Ian

[dian]

R8 --- 1 1/4 big end, 3/4 (about) taper engagement 7/16" (weenie) retention, no positive drive worth mentioning (the collet indexing screw doesn't count)

#40 --- 1 3/4" big end 1" small end 2 7/8 taper engagement, 5/8 retention (beefy) double keyed positive drive.

1 3/4^2 / 1 1/4^2 = #40 has about 2 x the rigidity

(by forrest addy)

its not so much about hp as about the rigidity of the machine, whether iso40 taper makes sence. if your considering some "knuckle-head" type with whimpy bearings, it might not. with an addapter your adding 4" of flex.

(disclaimer: i have never seen a r8 mill or used one.)

[old mart]

R8 is a good choice for hobbyists, much better than any Morse Taper, but if you have room and the power supply for a BT40 machine there is no contest. Plenty of tooling is available for the larger size, so that is no reason to avoid it.

[eKretz]

I hate R-8. I have run so many machines in shops that either have a mangled drive key or none at all. I have a QC30 on my machine but mine can use either those or NMTB30 with a power drawbar. Much better setup for me. Most Bridgeport sized machines aren't going to get max rigidity out of a 40 taper anyway, if you look at the actual shape of those spindles they put the tool interface quite a bit farther from the bearings because everything is larger and won't fit inside the quill. So more rigidity in the tool interface, less rigidity in the spindle. But that is dependent on the machine in question.

[Rich Carlstedt]

Again, looking in my parts drawer Rich? I have two sets there waiting for the transplant. My BP is already wired that way. The bearing sets? Dont ask, and they have to be a set, all three............I like the clamping or holding that the acura-grip and acura-flex collets have. And I have too many holders. So yeah, RF-45 type with a bad assed spindle. NOT
Its too slow. ....................... Its a spanner at the nose nut if you havent seen one. JR

JR, Yeah, You are looking at the King of Tool Holders ( Universal Engineering- Kwik - Switch ) and yes, I have about 35 of them on my Hurco , which is what Bob also has (Hurco) in his shop.
i have R8 in my Bridgeport , so yeah, I have two systems too--guilty !

Rich