Screw Machine Estimating 2

[Nate101]

Does anyone have information or know where to get some on estimating machined parts produced on a screw machine? I've quoted parts made on machining centers and lathes, both CNC and manual, but no experience with screw machines.
Thanks,
Nate

 

[rhodie]

Screw machining would be economical only if producing parts in large volumes.

When you are looking at designing and machining 6-12 discrete cutting tools for one part, the inital cost can be tough to swallow.

I am not sure of your part; perhaps the geometry might be achieved with stock cutters or off the shelf cutting tools, but even this would depend to the screw machine selected to run your part.

 

[Nate101]

So for cycle time do you quote only the longest running tool(multi spindle) or do you add the cycle time of each tool? Are all screw machines multi spindle? Are CNC screw machines faster to setup than manual? I want the speed of setting up a CNC machine but the economical prices of a screw machine to run quantities under a thousand. If anyone knows of any machines that may fit this, please enlighten me.

 

[griffengm]

Nate101,
For cycle time on a multi-spindle, we used the cycle time which equals the longest step. For single spindle, we used the time from one part hitting the pan to the next regardless of the number of steps.
I never set up a CNC so cannot comment on them.
As a rough rule of thumb one could say that the smaller, simpler the part, the smaller the run needed to justify a screw machine. However, a screw machine shop needs a bunch of such jobs to keep operating. We ran jobs as small as 100 pieces on relatively simple parts but they were justified because the cycle time was much shorter than if we had run them on an NC machine or CNC turn center. We also had capacity to fill.
The more involved the part, the longer it will take to set up and the more tooling/attachments will be needed. Special forms will take special tools and requires that the shop have toolmakers with slightly different skills than a CNC turning shop. One tool on a CNC can generate many different features where a screw machine may require several tools or a custom configured tool.
My experience was that it was generally easier for a SM operator to transition to CNC than vice versa.
Hope this helps some.

Griffy

 

[Nate101]

Thanks guys for the information. It's what I was looking for. I'd like to find more information on setting up screw machines, I haven't started looking for any yet though.
Nate

 

[griffengm]

Nate,
I am not certain of manuals on newer machines but the old Acme Gridley manuals were a short course in answers to all your concerns both managing and set up.
Good luck. I always enjoyed the challenges in working with these beasts. Managed and cared for well, they will give good return but woe to the shop that mistreats them. They can eat money faster than an eighteen year old girl with her daddy's credit card.

Griffy

 

[Nate101]

Don't say that, my daughter's turning 17 in a few days!! Thanks for the info. I'll start searching the internet. There's a couple of used machinery dealers out here. I may go see what they have. There was a couple of machines on ebay, I couldn't tell you if they were past their prime.

 

[griffengm]

Nate,
Not sure where "out here" is but two firms with whom I dealt were Jelinec in Ohio and Shorty's in Michigan. Both treated us well.

Griffy

 

[Nate101]

Thanks Griffy,
This is what I was looking for. The reason I'm asking is a friend of mine works for a company that out sources all their machining. They want to bring it back into the states. I told him I'd help find companies to make the parts, but I know nothing about screw machines. "out here" is Phoenix. I'll check out those two places while I'm surfing the web.
Thanks again
Nathan