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What to do before you buy your next new or used machine tool !

  1. Find the Right machine for the job

  2. Questions to ask salesmen

  3. Machines to avoid if Possible!!!

There are many things to consider when buying a machine, but here are some important considerations on machines to possibly avoid.

Do not buy a machine below serial # 100! Or the first ones off the line. Why?? There are many design changes, most of which usually have to do with coolant leakage or chips getting into places causing problems. Software and Ladder will have some quirky bugs and may not be updated unless you ask or have problems. Updates are not always available and can easily take 3-4 weeks or more to solve your problems. Replacement parts are also not readily available. Manufacturers say they heavily test them in their own market, but remember they do not abuse them as much as most people do. Remember some manufacturers start their serial numbers higher, so you may have to ask questions to try to figure out if the machine is a relatively new model. So, if you do not mind being a beta test site go for it and expect some problems.

Do not buy a full forth axis rotary table unless you really need it! Why?? Clamping is done on a smooth surface. There is not any tooth engagement for extra strength like a toothed coupling. The tolerance is extremely tight to get the unlimited indexing angle capability. This is why full forth axis are more prone to damage or in need of an alignment after a crash. Usually, the worm gear becomes oval shaped or the threads that is engaged gets damaged. Both of which will cause excessive load and servo alarms. Having a service tech come to repair or adjust the alignment will not be cheap or a quick fix. No, this is not covered ever under warranty. The other draw back is that if the programmer forgets to clamp it in the program, the only holding power is the engagement between the worm and worm wheel. It seems most machine tool builders have this weakness, which makes sense mechanically.

Do not buy a machine with an HSK spindle and tooling without some research! Many manufacturers have had problems with HSK type tooling design. They do have more rigidity and therefore hold tighter tolerances because of the greater surface area contact on the face and taper. Some of the problems that seem to be relevant are: contamination inside the clamping area of the tooling. Chips get between the face of the spindle and tool causing occasional run out in tools and problems with clamping. Spindles also lock up more easily because the drawbar clamping mechanism is on the inside of the tool. Often, the balls that drop in and out of the pockets can get wedged with any contamination. Then, when a tool change happens you break a cam follower or servo out because the tool is jammed. Good luck getting it unclamped. Alignment for tool changer is also more critical compared with BT or CAT tool holders. This is because there is not much of a taper for the tool to center itself as it goes in therefore requiring a lot more tool changer alignments after small crashes. Which is the right thing to do anyway, but most companies just change offsets and go. Also, the groove in the tool is sometimes smaller (HSK30 taper) and therefore chips get wedged causing the tool to be thrown during tool change because the alignment will be off or not seated in the arm. Aluminum chips from large face mills cause the most problems. Mainly because aluminum is very light and sticks to everything.

Before you buy, ask to go to customers to look at their process. Observe the nooks and crannies where chips are thrown and build up. Also ask to see their service report file folder on that machine if they have one.

Avoid Machines that are special order Self explanatory! Hard to get everything, parts, service man with experience on machine, software bugs and unproven design. Ask to see the machine at another customer at a minimum.

Choosing the right machine for the job

Size of working envelope: table size, tool clearance, chuck size and tool change swing clearance
Tool capacity
Type of tool holders
used CAT/BT/HSK (less cost or availability)
Machine horsepower (for cutting force)
Type of machine control (easier on operators less collisions)
Compatibility with existing CAM software (or programs already written)
Number of machining axes
can you run other jobs on it if the another machine is down?
Fixtures determine length, width, height, how many parts in one cycle to determine size of machine.
What is the cycle time if the operator is running multiple machines? You may not need that extra second for a better fitted machine.
Considerations you may also consider on using this machine as backup for other jobs incase you need to wait 3-4 weeks for replacement parts. Also, consider buying 2. To have an extra machine to swap parts for troubleshooting can save you a lot of money.
Automation/integrations -How easy is it to get this done, either through the dealer or integrator. Can vary big time in actual costs for this. It may also be cheaper to ship machine to integrator to automate, so ask if this is an option for you.

Questions to ask your salesmen?

What machines do you sell the most of? These will have the bugs worked out and therefore, the least amount of problems and most parts available.
Can I get a time study? Only ask for an approximate cycle time for this. If you are more serious ask for a real time study that is more accurate. They will less likely help you out in the future if they think they are doing this most likely for nothing.
Can I have a part run to determine actual cycle time or get a turn key? Many times they will run an actual part as long as you agree to purchase the machine if the cycle time is below an agreed upon time.

Can I see this machine at another customer? There is nothing like looking at something before you buy. Look at the machine, pretend you are the operator and see how easy it is to perform everyday tasks. If you can look to see what they are cutting, look for chip build up that can cause problems. Check if they are using large face mills, which cause the most problems.

Penalty clauses- If a salesmen lies to you about delivery to get the sale, or promises a certain cycle time that can't be achieved, that is going to hurt your business and possibly cause you to lose the contract. Think about a penalty clause, only after you agree on a price and a guaranteed date of delivery, present a penalty clause to the salesmen and tell them this will be required to get the sale. Make sure you present them with your reasons for proposing this clause they should understand, ask them if they were the owner, would you do the same thing?- Most likely the answer is yes. They will ultimately have to go to their manager or manufacturer to find out if it is possible. The clause should consist of either a percentage of the machine cost or a fixed value at a certain interval up to a maximum percent. Unfortunately, one thing you have to understand is it is very hard to get the exact dates of delivery. Not all salesmen are trying to screw you for the sale. They may however, stretch the truth so make sure you ask the right questions.

Machine tool help & advice before you buy your next machine tool. You have learned what mistakes to avoid and what to look for when considering CNC machine purchase.