Best Way to Machine Cast Aluminum Cable Drums?

North Design · Apr 19, 2020

I need to have some cast aluminum garage door cable drums machined. I would like to ask the community for advice on the best way to approach this before I post the job for bid in the Manufacturing Resource section. The selected cable drums have a 12 foot cable capacity but I need about 22 feet capacity. I cannot use the larger drums as they will not fit.

My plan is to mate two drums together to increase the cable capacity, to do this I need the following. The left drum would have it's right flange removed and the right drum will have it's left flange removed. The two machined halves will then be mated on a shaft. In order to make sure the wire rope cable runs seamlessly across the joint they both will need to be machined to a common alignment point such as the shaft keyway. In other words, a common location to allow for both the left and right cable grooves, peaks and valleys to mate up and allow the wire rope cable to run seamlessly across the joint.

I will need four machined drums per system, if the prototype turns into a viable product I would order perhaps 20 pieces at a time. So my questions are what is the most cost effective method to achieve this, CNC machining or a different method? Any and all advice is greatly appreciated.

Here is a example photo of the cable drum:

Garwood · Apr 20, 2020

I don't think your 2 piece with keyway deal is going to work.

Those drums are the adjustment to align your door in the opening. That's how you set and adjust the cables.

I would make them from solid using a CNC lathe and a mill.

North Design · Apr 20, 2020

Hello Garwood,

Thank you for your reply, sorry I was not more clear on my use. These will not be part of a garage door but part of a hoist, I'm trying to stay with commercial parts where possible to minimize recurring cost per unit. I want to give the machined drums a chance first in my prototype and if it does not work out I may need to have them fabricated.

What would you think the price range would be to have them fabricated, the single unit would be about 4" diameter, 4.5" long?

Back to the original question, what would be the most cost effective method to machine these, CNC or something else?

Thank you

Garwood · Apr 20, 2020

North Design said:
Hello Garwood,

Thank you for your reply, sorry I was not more clear on my use. These will not be part of a garage door but part of a hoist, I'm trying to stay with commercial parts where possible to minimize recurring cost per unit. I want to give the machined drums a chance first in my prototype and if it does not work out I may need to have them fabricated.

What would you think the price range would be to have them fabricated, the single unit would be about 4" diameter, 4.5" long?

Back to the original question, what would be the most cost effective method to machine these, CNC or something else?

Thank you

What does CNC or something else mean? You're going to have to machine these. If you find some guy says he can make that with a coat hanger two rocks and a hammer your probably not going to have a successful product there.

If you're making one of each you are going to pay a lot for that. You need to draw it and design it to be easily made.

I think the questions you need be asking are not "How can this be made", but rather how can you design it so the machining doesn't eat your wallet. If the drum had a constant diameter that would reduce the cost and make it something most machine shops could make.

The part you have is a die casting made by the millions. Your new part will not be a casting.

North Design · Apr 20, 2020

Garwood said:
What does CNC or something else mean?

I was just trying to understand which machine in the shop is the best for milling down cast aluminum. CNC Mill, Manual Mill, Grinder, or some other machine tool?

michiganbuck · Apr 20, 2020

I think your method should work with two (R&L) on a common shaft and trimmed until the cable thread matches, scalp out some divets and weld perhaps 6 or 8, 1" welds, then even/trim by hand trim the welds to make the constant cable thread form.

or ...

Weight dosen't matter so they could be machined from solid bar stock on a CNC of conventional lathe, and the cable end lock just hacked in by hand..

Im not a welder so likely I would just turn then on a lathe ,but what is the thread per inch from here looks like a 3 or 4 TPI.

Yes need bore out the indent for set screws if they need to be hidden..no problem.

No I don't want the job but it looks easy.

*But It looks like 8" aluminum bar stock costs a fortune likely for made parts would be price wise.
*Standard Lift Garage Door Cable Drum Garage Door Parts D400 96 Overhead Repair | eBay

sfriedberg · Apr 20, 2020

North Design said:
I was just trying to understand which machine in the shop is the best for milling down cast aluminum. CNC Mill, Manual Mill, Grinder, or some other machine tool?

Would you consider "the lathe"? Put a drum on an arbor, remove the flange, piece of cake. If you need the cable grooves "timed" to each other, you figure out the finished length ahead of time and put a locating collar and key on the arbor so the untouched end of the drum is always at a known location, then face the other end of the drum to length.

Speaking as an engineer, I really don't like the idea of butting two cantilevered drums up against one another and calling it a wider drum. But that's a design problem, not a manufacturing problem.

bigjon61 · Apr 20, 2020

CNC Lathe for sure. Couple of design considerations would be 1 piece out of bar stock, and add additional material to the open end of the sheave to allow for the appropriate size set screw. Also, no funky keyseat sizes. There are standards for key sizes in relation to shaft diameter, please use them. Other than that it looks like a pretty straight forward design plan.

You will probably have better luck making these that way rather than cutting/welding/grinding the existing ones.

michiganbuck · Apr 20, 2020

But it looks like 12” aluminum bar stock is about $1,000 a foot.
I guess one could run a threaded tube/bushing through the welded part to give it more strength, perhaps with loctite.
(yes with the key way cut out)

12' Garage Door Drums D400-144 Torque Force Torsion Spring Overhead Doors Repair | eBay
MetalsDepot(R) - 6061 Aluminum Round Bar - Shop Online!

Garwood · Apr 20, 2020

michiganbuck said:
But it looks like 12” aluminum bar stock is about $1,000 a foot.
I guess one could run a threaded tube/bushing through the welded part to give it more strength, perhaps with loctite.
(yes with the key way cut out)

12' Garage Door Drums D400-144 Torque Force Torsion Spring Overhead Doors Repair | eBay
MetalsDepot(R) - 6061 Aluminum Round Bar - Shop Online!

A 12' bar of 12" 6061 is about $3000 give or take. He needs 4" round bar. Should not be a problem.

In a garage door app those drums tighten down onto what is essentially EMT. They just crush the tube a bit and they don't spin. If using on solid bar I would mill some flats.

Peter from Holland · Apr 21, 2020

North Design said:
My plan is to mate two drums together to increase the cable capacity, to do this I need the following. The left drum would have it's right flange removed and the right drum will have it's left flange removed. The two machined halves will then be mated on a shaft.

You cannot mate a left hand thread with a right hand thread
you need eighter 2 left hand drums or 2 right hand drums

Peter

michiganbuck · Apr 21, 2020

And mating the right and left the key way would not match at the same place where the cable thread make match.

Red James · Apr 21, 2020

The machine required would be a lathe; manual would work fine for prototyping. Should be a simple matter to trim lengths to match grooves, but your total length could vary by 1/2" or so.

Another problem to solve is 'How to keep two piece pulleys tight together, as the wire rope tension will try to push the pulleys apart.

Peter from Holland · Apr 21, 2020

michiganbuck said:
And mating the right and left the key way would not match at the same place where the cable thread make match.

You could trim lenght so they match

Peter

michiganbuck · Apr 21, 2020

Could lathe turn the cable thread completely off a low price pair of standard drums, cut to needed length making a R&L half, press or loctite a tube on/over the one half, press or glue the other half, and then turn a new cable thread. Yes doing this with key way in line. the key way would give some strength to the assembled drum if the key is full length(?).

The overlay tube might be made of aluminum or steel pipe if a standard pipe might be found..even brass pipe.

If room drill and tap center hub for two or three long screws. might loctite the screws as they need never come out. This seems the low cost method if turning would fit a standard tube with little or no ID boring of the tube. likely the drum OD would not need +- .030 or 1 mm. close.

michiganbuck · Apr 21, 2020

michiganbuck said:
Could lathe turn the cable thread completely off a low price pair of standard drums, cut to needed length making a R&L half, press or loctite a tube on/over the one half, press or glue the other half, and then turn a new cable thread. Yes doing this with key way in line. the key way would give some strength to the assembled drum if the key is full length(?).

The overlay tube might be made of aluminum or steel pipe if a standard pipe might be found..even brass pipe.

If room drill and tap center hub for two or three long screws. might loctite the screws as they need never come out. This seems the low cost method if turning would fit a standard tube with little or no ID boring of the tube. likely the drum OD would not need +- .030 or 1 mm. close.

If in doubting of strength might add three spokes welded in the core.

North Design · Apr 21, 2020

Thank you everyone for all the great tips and the suggestions on using a lathe, excellent idea and I see how it simplifies the job vs. a mill. I'll summarize my plan going forward. I will be a using garage door shaft and keys so everything mates up.They make the shafts in several gauges and even solid so strength will not be an issue. I will provide the machinist with a piece of shaft and keys so the drums can be mounted and then put the shaft into the lathe arbor. There will not be any need for cutting/welding/grinding to mate the two together, that will be achieved as follows.

Once faced I will mount the first drum on the shaft and tighten the hidden setscrews. Then the second drum will be butted up to that and those setscrews tightened. During testing of the Prototype I will monitor the two drums to see if the wire rope is pushing the drums apart.

The OD on the large section of the drum is 4.8" so if being turned from scratch it would require 5" stock ($152 per foot). By the time you add in labor and needing two or four per system it becomes cost prohibitive for this product, that I why I going to see if the commercial drums will work in the Prototype. Thank you to everyone for your help, oh yes, no coat hangers, rocks or hammers needed, since this engineer knows how to tell the difference. :cheers:

DDoug · Apr 21, 2020

North Design said:
Thank you everyone for all the great tips and the suggestions on using a lathe, excellent idea and I see how it simplifies the job vs. a mill. I'll summarize my plan going forward. I will be a using garage door shaft and keys so everything mates up.They make the shafts in several gauges and even solid so strength will not be an issue. I will provide the machinist with a piece of shaft and keys so the drums can be mounted and then put the shaft into the lathe arbor. There will not be any need for cutting/welding/grinding to mate the two together, that will be achieved as follows.

Once faced I will mount the first drum on the shaft and tighten the hidden setscrews. Then the second drum will be butted up to that and those setscrews tightened. During testing of the Prototype I will monitor the two drums to see if the wire rope is pushing the drums apart.

The OD on the large section of the drum is 4.8" so if being turned from scratch it would require 5" stock ($152 per foot). By the time you add in labor and needing two or four per system it becomes cost prohibitive for this product, that I why I going to see if the commercial drums will work in the Prototype. Thank you to everyone for your help, oh yes, no coat hangers, rocks or hammers needed, since this engineer knows how to tell the difference.

See if they push apart ? You can simply calculate those loads, resulting vectors,
dia. of wire, tension....1st year stuff.

Life cycle testing is needed here.

But as an engineer you should have know that....

North Design · Apr 21, 2020

digger doug said:
See if they push apart ? You can simply calculate those loads, resulting vectors,
dia. of wire, tension....1st year stuff.

Life cycle testing is needed here.

But as an engineer you should have know that....

Close, I was simply repeating back some of the great points others made in the above posts.

Your point is well taken but when working on a proprietary design, and discussing some sub-elements about it in a public forum, it's not a good business practice to discuss all the details, I think you understand.

neilho · Apr 22, 2020

Maybe a little late, but what you describe is only one way to do it.

I spend a fair amount of time dealing with people who want me to build/make things their way. I often wonder why they don't do it themselves, if they're so sure. Sometimes they're absolutely right, it's the best way. More often, they don't understand the process and there's a way to make it simpler/better and save them money. I'm dealing with an engineer right now that has mocked up a complicated bracket where a simple strap will do.....

Suggesting this method to your machinist, then asking his advice would be more likely to get the most from him.The initial approach is important to a good outcome.

Best Way to Machine Cast Aluminum Cable Drums?

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