if you have a big lathe, can you tell me the diameter of the rod in your banjo please

[dustin wassner]

I am in the process of building a lathe and am working on the banjo. Trying to use the cam lock design seen on many lathes, and am wondering what diameter rod to use to span the ~16" length of the banjo. If you have a Robust, Powermatic, OneWay, etc, could you tell me what the diameter of the rod is on your banjo. Thank you in advance.

[CHARLES D Richards]

Assuming you're referring to the tool rest hole and post that fits into the banjo? The Powermatic 3520 has a 1" post opening

[John Keeton]

I believe the OP may be referring to the "tool support rod" which runs under the banjo. http://www.ereplacementparts.com/powermatic-3520b-1352001-tefc-2hp-220v-woodturning-lathe-parts-c-32549_32637_32638.html

[dustin wassner]

thanks, but what I am referring to is the rod in this picture
http://www.penturners.org/forum/attachments/f167/47318d1299712582-powermatic-3520a-banjo-banjo5.jpg

[Steve Schlumpf]

Robust AB is 1.25".

[dustin wassner]

wow that is bigger than I expected. I thought it would be 7/8" or 1" at most.

[John Keeton]

The Laguna Revo 1836 has a 1" rod.

[Brice Rogers]

The locking rod on my G0766 (a fairly big lathe) is roughly 3/4 inch in diameter. I am away from my lathe right now - - otherwise I'd give you a more precise number. But the C-clip at each end is spec'd on the parts list as 19mm. So that gives you a fairly close number.

You may consider going on-line with Grizzly and checking out their parts ordering. You can buy all of the major parts for their banjo for under $80. For example, the casting is 48 bucks, the rod is $18, etc.

I think that the confusion is that several posters (like Steve S.) were commenting on the diameter of the tool post. The Griz tool post is 25 mm but 99% of the owners bore it to 1".

[Don Bunce]

The rod on the PM3520b is 34 mm, or 1.3385 in.

[Brice Rogers]

I think that Don Bunz is referring to the tool post diameter too. When I look at the picture of the banjo on the PM website I can see that the tightening rod is smaller than the tool post. A larger diameter tightening rod will work, but it will raise the height of the tool post and in some situations will limit the diameter of what you can turn.

If you can go to someone in your area or to a Rockler store (or equivalent), bring a mic or a caliper and measure. Otherwise, you are going to be sizing the tightening rod to the dimensions of the tool post.

http://images.powermatic.com/image/1352001_det7?hei=480&wid=480&fmt=png-alpha

[Don Bunce]

The tool rest post is 1" dia. The rod under the banjo, which is what we are talking about, is 1.338 in.354649

[Olaf Vogel]

I am in the process of building a lathe and am working on the banjo.


So you are building a banjo from scratch?
Would you be able to post pics / plans etc?


Because I need to custom build one for my lathe. its very old and I can’t find a suitable size on the market, so it will be DIY.


Thanks

[Brice Rogers]

Don Bunz: I stand corrected. And "Holy Moly" that shaft is wide!

[Dale Winburn]

I made my banjo with 1" round bar stock.

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[dustin wassner]

thanks for all the repsonses.

Dale, what is the length of your banjo? I am looking to make one roughly 15" long and was hoping to go with 1" 4140 as I thought it would be stronger. But there have been enough replies to this thread with larger diameter rods than 1" that I am concerned that if I use 1" it will bend if the eye bolt is in the center of the rod when clamped.

[Dale Winburn]

The total length of my banjo is 12", I get very little deflection even when the eye bolt is in the center. The banjo works well for my use. I maybe would go 1 1/4" with a 15" banjo.

[dustin wassner]

thats what I was thinking, especially after seeing what the american beauty and powermatic is. what are your thoughts on cold rolled normal steel ($20) vs cold drawn 4140 (37$)? For what its worth, I am already over budget with the project...

By the way Dale, the homemade lathe on your website was the first I ever saw like this and was the initial inspiration to decide to make my own. So, thank you.

[Dale Winburn]

My bar is cold roll steel, don't know much about types of steel so can't help you there. Thanks for your comments about my homemade lathe, it still gets a lot of use. I have recently upgraded my bed to an 18 inch bed and variable speed three phase motor with VFD.

[dustin wassner]

thats great Dale. I did this exact approach with mine. What frequency are you able to drop to? I have read about overheating the motor if running at a low frequency for extended periods of time, but I have never heard anyone who says this define what an extended period of time is.

[Olaf Vogel]

thats great Dale. I did this exact approach with mine. What frequency are you able to drop to? I have read about overheating the motor if running at a low frequency for extended periods of time, but I have never heard anyone who says this define what an extended period of time is.

Hard to define. If the motor is working against a lot of resistance at low speed (hence pulling a lot of amps), then you risk overheating.
I use very precisely calibrated solution:

1 - put my hand on the motor - during normal operations - feel the temps
2 - when running slow, retest and compare.

:)
Or you could hook up thermo couples with digital meters.
If you are concerned, get a strong fan and blow it over the motor to reduce temps.

BTW - a good way to cool down most motors, is to take off the load and run them at full speed.
That gets the air flowing and resumes normal cooling.
(not sure if the works for fully enclosed motors)

Stopping and waiting is not good - the heat just builds up.

[dustin wassner]

that is precise...

a thought: when I look at the american beauty/powermatic/etc motor and rpm ranges stated in their manual, they are all using vfd with ac motors, and on their low gear setting, the low rpm divided by the high rpm for that gear setting is pretty consistently 4%. I am not sure if this means that they are turning the frequency down to 4%, assuming running at 100% frequency equates to the highest rpm in the given range for that gear setting. I also did not ready in any of their manuals that running the motor for long periods of time with the frequency turned all the way down would do damage. If they are in fact going to 4% frequency, I am unnecessarily worried, as I was concerned that dropping to 15% frequency would cause overheating.

[Dale Winburn]

My motor will go to zero rpm, never had a problem, but when I'm running for long periods at low speed I do as Olaf suggest and feel the motor. My motor is an inverter duty motor (made for use with a VFD).

[Michael Schneider]

Dustin,

Hard to give number. The insulation grade of the motor will determine slow/torque of motor. Insulation grade of "F" is the best grade available at a reasonable price. Insulation grade of "F" are usually tagged inverter grade. It is not exactly what you are looking for but if you have not bought your motor yet, buy one with an insulation grade of "F" for high grade insulation that can handle the heat of low speed and high torque.

Note: Insulation class of "H" is the best, but it is very high $$$$, and likely not necessary.

Have fun.

Michael

[Leo Van Der Loo]

What you guys are talking about is NOT a banjo camlock, but just an excenter shaft that will deflect if not thick enough, actually most all of them will if clamping the banjo tight.

A banjo like Oneway uses has the camlock in it, and the banjo itself is where the forces are applied to, it will not bend or sag, patented as well, I don’t think any of the other lathes have it.

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[dustin wassner]

thanks, Leo. I did see a video that describes how the OneWay design is different than the others. But I think with my limited tools it is not an option unless I can buy the cam and shaft separately. I have the part #'s 3811 for the cam assembly and 2702/2409 for the shaft, but am unable to find anywhere that sells them. Any idea where I would find them?

[Leo Van Der Loo]

thanks, Leo. I did see a video that describes how the OneWay design is different than the others. But I think with my limited tools it is not an option unless I can buy the cam and shaft separately. I have the part #'s 3811 for the cam assembly and 2702/2409 for the shaft, but am unable to find anywhere that sells them. Any idea where I would find them?

As usual you order parts at the manufacturer, Oneway, they have a 1-800 number.

Are you able to machine the ledge in your banjo housing, the camlock needs that to work.

[Brice Rogers]

I am finding all of this information interesting. I own a Griz G0766 and this is the first time I've had a cam lock banjo. I didn't realize that there are several different approaches.

On the Griz 0766 they use a sliding cam lock. The locking rod has a longitudinal slot in it for the eccentric cam mechanism to slide on. If I were making a duplicate, I think that I would find the machining of the slotted cam a challenge.

I like the idea of square shaft that Leo posted (One way). Seems like it would be easier to fabricate.

I also like the approach posted earlier for the PM where the shaft is round, uses an eyebolt and the ends are off-axis. Seems like it would be easy machine with a lathe and a 4 jaw chuck.

[dustin wassner]

Brice, can you post a pic of your banjo design?

How would you go about fabricating the oneway design? I am trying to wrap my head around it but think it would be easier to just use the solid round rod the entire length.

[Dennis Ford]

The Powermatic at full speed is 120 hz (which is double normal 60hz power)


that is precise...

a thought: when I look at the american beauty/powermatic/etc motor and rpm ranges stated in their manual, they are all using vfd with ac motors, and on their low gear setting, the low rpm divided by the high rpm for that gear setting is pretty consistently 4%. I am not sure if this means that they are turning the frequency down to 4%, assuming running at 100% frequency equates to the highest rpm in the given range for that gear setting. I also did not ready in any of their manuals that running the motor for long periods of time with the frequency turned all the way down would do damage. If they are in fact going to 4% frequency, I am unnecessarily worried, as I was concerned that dropping to 15% frequency would cause overheating.

[Don Bunce]

The Oneway design looks interesting, but wouldn't lend itself to DIY easily, and I don't see where it would have that much advantage over a traditional round bar as long as you use an adequate size bar to start with. I wouldn't use anything less than 1 1/4".

[Leo Van Der Loo]

The Oneway design looks interesting, but wouldn't lend itself to DIY easily, and I don't see where it would have that much advantage over a traditional round bar as long as you use an adequate size bar to start with. I wouldn't use anything less than 1 1/4".


I assume you never used a Oneway banjo, maybe you should try one or talk to those that do use one, and no not an easy DIY project, the reason some do buy a Oneway banjo for their lathe with some less that ideal Banjo.

[Brice Rogers]

Dustin, I am out of my shop right now. If you're interested I can post some pictures on Monday.

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This is a section of the parts assembly drawing from the Griz web site for the G0766. The tightening rod, 52V2, has a slot longitudinal. (I don't own a slotting saw or a 0.062 mill). This groove or slot corresponds/aligns with a protrusion in the inside of part 60. Part 60 is eccentric. (Two round circles offset from each other). So when you rotate the rod it causes the eccentric to rotate within the equivalent to the PM eyebolt, part 59 and it pulls part 59 upwards, locking the banjo.

Griz uses a round washer which (I think) will long-term get some wear. I think the One-way design with the square plate is better. When/if my griz washer gets chewed up, I'll replace it with a square plate.

If I were trying to make this, I would consider buying the parts from Griz for under 80 bucks. The protrusion on the eccentric would be a challenge to machine. I think that Griz used a special broach. I would have problems with that. It might be easier to slot it (the opposite of a protrusion) and put in a keyway anchored with superglue.

I think that the One way design would be easier to duplicate and is just plain better. But you are going to need a mill and a metal lathe to make it too.

What do you have for metal shop equipment?

[Don Bunce]

Leo,
You are right, I have never used a Oneway lathe, but the Powermatic banjo has never come loose while turning, so to me it is a moot point that the Oneway may be better.

The OP mentioned that he had limited tools available, and had already gone over budget, so in his case, a round rod system would seem to me to be a better solution.

[john taliaferro]

Yes Leo is correct , i made mine like oneway's it locks tight .Their $ on just a banjo is not to bad either .

[John Keeton]

I have no doubt the Oneway design is superior to others using rods, but a properly adjusted banjo should hold fine for the forces at play. I have never had an issue with my various lathes.

[dustin wassner]

would this mean that an 1800 rpm motor will do 3600 rpm at 120 hz? If so, how would i find out if my motor can do this, and is there any risk to it?

[dustin wassner]

I see the biggest advantage to the oneway being: 1)lighter weight, as a smaller square bar can be used and deflection is not a concern, 2) tighter clamping ability, which may be unnecessary since the solid round bar design works fine on other lathes, and 3) bragging rights when marketing their lathe with a unique patented design. I have used a powermatic in the past and it clamped tight, but never gave banjo design a concern when using it. I will be using a vicmarc vl300 at an acquaintances house tomorrow and will get an idea of what their banjo design is.

the oneway 24" swing toolrest sells on their site for 291 before shipping. To each their own, but that is waaaay more than I am about to spend on a banjo...

I am still waiting to hear back from oneway for a price on the cam mechanism as I cannot come up with an idea of how to fabricate something. If I could find a ~2"-3" long sleeve with a square hole the entire length, I'm pretty sure I could make it happen. I even considered welding two 3/4" drive sockets face to face, but I think the square needs to be a little smaller, and I have never seen 5/8" drive sockets...

[Leo Van Der Loo]

I have no doubt the Oneway design is superior to others using rods, but a properly adjusted banjo should hold fine for the forces at play. I have never had an issue with my various lathes.


I’m sure it depends on what you are turning on your lathe, and the forces that are used to do that, I do know at least a few turners that did exchange the Banjo of their lathe for a Oneway Banjo.

Just consider doing some metal spinning and that with the banjo of your lathe, there is also the clamping handle being at the same position every time and not sitting higher or lower depending the flexing of a round bar banjo.

Picture of a Nova with a Oneway banjo.

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