Machining Parts – What’s it all about & Why is it so expensive?

I thought it would be a good idea to enlighten those uninitiated into all of what happens in the making of a machined part. I found it a fascinating and an illuminating process. Not realizing or appreciating what looked so simple, even automated, could generate so much work and such an expensive price tag. So many times we get sticker shock from what we thought was an easy or automated process and wonder what is going on. Are we being taken to the cleaners? It can certainly feel that way at times but the reality is making “1 off” parts is a very expensive endeavor. You need to understand and accept this to be prepared if you are going to take my plans (or anyone else’s) to your local machinist to do some work. So lets start off with an FAQ of sorts about getting parts machined and then we will work out a concrete example from this build so you will understand what I mean.
***Disclaimer***: I am not a machinist nor do I play one on TV (or work for one). The experiences described below are from my personal experiences/lessons learned from dealing with several machine shops both local and distant (out of state) to the DFW area. This discussion is designed to help you understand what you are getting into and is not to be considered the only or definitive authority on the subject. Your experiences/mileage may vary. Lets start off with what you will be faced with when dealing with most machine shops.
Machinist Expenses
Setup Fees – The cost of entering measurements or dimensions into machines, etc. There is usually a minimum charge that shops assess. For example, TAP Plastics charges a 250.00 minimum fee for anything cut on its CNC machine.
Material Fees – The cost of the material used in its raw state
Machine & Labor time – Time charge for machine operation & operator monitoring/adjustment
Sub Contractor fees – Using other shops for completion like anodizing or welding parts together.
Shipping & handling charges – self explanatory.
Taxes – self explanatory.
Machine Shop Expectations from the Customer
Clear, complete communication. He will only do what you tell him to do. He doesn’t read minds!
When you come into a machine shop you should know “what” and “how many” of a given item you want made. You also should know what you want it made out of like aluminum, plastic, steel, brass, etc). Not having or knowing this information puts the machinist in a consultant capacity. His time is Money. Don’t think for a minute that he wont charge you to discuss how to do something if you do not already know what needs to be done. A good machinist SHOULD discuss what you are wanting done but don’t go in there with the expectation that he is going to figure this stuff out for you for free and then only bill time and materials to make it. This is why a lot of machine shops will not deal with hobbyist for “1 off” projects or why requests of this nature are routinely done when there is no other work available.
You need to have clear, accurate drawings with exact measurements clearly identified. They do not have to be CAD drawings but those are the best to eliminate confusion and mistakes.
It usually does not matter if you have CAD drawings in a computer file or not. Good machinists can take a pdf or print outs of some type and work with that as well. However, no matter what you have as a reference, there will be a degree of human involvement required to get that information from the source into his machines and this is where the setup fee is based. In some cases the setup fee can be more than the cost of the material and labor combined to produce your part. The “key” to keeping your costs down is by dealing with a machinist that has already done the setup for this part if at all possible.
What is a “1 off” part or project? Quiet simply it is the making or the machining of any part or assembly where there is only a quantity of 1 involved. For example, A left and right hand version of something is still considered 1 item. There could be 40 different components to be made in the assembly of 1 item. That is still considered 1 item. This is the most expensive cost per item there is. Often, if you inquire, you could get multiples of that item you are making for only a fraction of what you had to pay for just 1. This is the basis for doing “runs” of parts so that others can benefit from the lower cost and availability.
Also, some shops will require you to put down 50% of the expected charge before they will begin to schedule or perform any work.
Customer expectations from a Machine shop
Clear, complete communication – Don’t assume anything! Ask a lot of questions!!
Clear explanation of rates/fees – Make sure you ask for a detailed billing/charge list of services.
Authorization before action – No Shop should just go blindly ahead unless you authorize them.
Detailed billing – A complete, clear and accurate listing of item, cost, time and quantity.
Approval before payment – You need to make sure you are happy with it before payment. The
shop should work with you if there are any issues with quality or quantity of work performed.
Delivery Promises – Discuss at the very beginning any time lines you need to hold the shop to and make an agreement with them what will be done if they fail to meet that promise (like a discounted rate). Get it in writing. Shops have been known to do what is in their own best interests but if what you are contracting them for is time based they need to know that up front and that what they have or have not done maybe at risk if not delivered as promised. Recognize that some shops will not do business with an individual this way. That may be your clue to take your business elsewhere. You need to be reasonable when negotiating on this point.
A Practical Example:
Lets take the original aluminum waist plate I made for my B9. It started out as a block of solid 25 lb sheet of aluminum. The outside configuration/drawing was a copy of the PVC version of the waist plate that Andy Schwartz currently sells. The plate of raw aluminum currently runs at approx 4.20 per pound for 6061. It took (with a CAD drawing as a reference) 1hr to input those figures into the CNC machine. Most shops charge between 60-75/hr to do that. While the CNC machine is cutting the aluminum the CNC operator must monitor the process to watch out for broken bits, misalignment or other errors. Then he has to take that device out and flip it around and restart the process all over again to complete the project. That cost me 225 for time and 125 for materials equaling $400.00 dollars.
Now take that 1 step further and lighten that same waist plate. Instead of having dozens of data points to enter into the CNC machine, you now have hundreds of data points to enter into the system. All having to do with length, height, width and depth. The additional programming to do the diet version required 3 additional hrs of programming. To do all of this 1 time would of cost you $825.00 for 1 waist plate.
As you can see, the amount of time expended for that 1 waist plate makes it very costly. Now if you made more than just 1 of those waist plates the setup would only need to be done once. The other copies would only incur material and time charges, in this case it drove subsequent diet waist plates prices all the way down to 425.00 each; which is the price you would pay now.
I hope this makes sense to you and allows you to further appreciate what I have done for the club (for these parts) and the beauty of mass production.