Mitek training

The Mitek CNC Mill is an excellent tool for general purpose milling of any machine shop compatible material including plastics, aluminum, steel, stainless steel.

There is no woodworking permitted in the machine shop. If you would like to CNC mill wood, use the Shopbot.

Mitek Training

Mitek training costs $150. Case-by-case exceptions can be made for those wishing to learn but for whom that fee represents a hardship. Contact Shakeel on Slack.

The CNC machining skills you will learn by the end of the training:

1. An easy to learn way to manufacture parts which require multiple types of tooling (This can be cumbersome for complex parts and can reduce your precision. It is generally possible to make metal parts to within 0.015 inches using this method if you are careful. More advanced users may elect to figure out how to manage tooling in the CNC software.)
2. Adapting drawings for the CAM process.
3. Mounting complex shaped parts on the CNC without the need to make soft jaws.
4. Managing coolant and lubrication on the CNC
5. Listening to the CNC to know how to modify your pre-programmed machining process on the fly

Prerequisites

The Mitek is in concept an automated version of the Bridgeport manual mill, however the dangers of using the Mitek are amplified. To be trained on the Mitek, you must have completed a Machine Shop 101 course on the mill and used the manual mill for at least 50 hours. Other demonstrations of proficiency such as pictures of completed projects or other evidence of experience operating a manual or CNC mill are generally acceptable and are evaluated on a case-by-case basis.

You should own your own cutting tools that you will use during the training, though the instructor should also have them available. Cutting tools can be made from any material appropriate for your application. For example, if you only ever plan to use the Mitek to cut plastic get whatever tooling is cheap and make your certification part from plastic instead of aluminum. Shakeel really likes the endmill set sold by Harbor Freight which is priced competitively and has stood up to plenty of aluminum and steel machining on the Mitek and the Bridgeport. Carbide tools are great, but they're expensive and easy to break on the CNC where you won't get a lot of force feedback letting you know that you're feeding too fast. Roughing endmills are also great. Recommended cutting tools:

1. 1/4" endmill
2. 1/2" endmill
3. Center drill appropriate for a 17/64" drill
4. 17/64" drill

This course uses an aluminum plate 4" x 4" x 1" to make the part from. A smaller plate can be used, but for learning purposes make sure that your cut depth for making the logo is half the thickness of the plate. If you make the lateral dimensions of the plate smaller, ensure that you have a sufficiently small endmill that will fit in the slots that need to be cut. Your endmill should be at least 25% smaller than the slots you are attempting to cut in this part.

Software

The Mitek operates using a digital instruction set that must be pre-programmed into the machine before you begin. This is colloquially known as G-code. G-code is almost never manually programmed from scratch and is typically generated from CAD software packages in combination with CAM tools. CAD tools will allow you to create a drawing of a part, CAM tools will allow you to generate the step-by-step instructions for CNC tools to make the part.

You have two options for CAD/CAM packages for this course.

At the moment, Shakeel is most familiar with Solidworks as the CAD software package (you can obtain a free license through Tinkermill) with the free HSMXpress add-on acting as the CAM tool. While Solidworks does include an integrated CAM tool, it does not have a free post processor which is compatible with the Mitek (the post-processor is a file which provides instructions for the CAM tool with how to communicate with the CNC). HSMXpress is limited to 2.5D parts machining.

The other available option is Fusion 360, for which you can obtain a free license for personal or small business use. Fusion 360 uses the full HSMWorks CAM engine HSMXpress is based on and is able to do full 3D machining and may be a better long term option. This section may be updated once Shakeel learns Fusion 360.

You can use the standard Vickers Acramatic postprocessor bundled with HSMXpress. Richard Warner has a custom post processor that he wrote for the Mitek but Shakeel has not tested it yet.

If you have other tools which you prefer to use for CAD or CAM you are more than welcome to do so, however the ability of the course instructor to provide support may be limited.

Users have experienced syntax errors when transferring G-code from MacOS computers to the CNC. The exact same G-code transferred from Windows has avoided these syntax errors. Using a Windows computer for the file transfer is therefore recommended.

Getting trained on the Mitek

The procedure for getting trained on the Mitek begins with a self-directed and ends with a training on how to operate the Mitek and the manufacturing of a demo part.

Self Directed Component

The purpose of the self directed component of the training is to familiarize yourself with CAD and CAM software tools. At the end of the Mitek training, you will have made a version of the Tinkermill logo out of aluminum. You can obtain the 3D model for the Tinkermill logo cut into aluminum here. LINK TO FILE. The goal of the self directed component is that at the end, you should have a full set of CAM instructions and manufacturing steps to make this part.

To manufacture this part, you must perform the following operations:

1. Mill the logo into the aluminum block
2. Drill the mounting holes for the jig plate into the part
3. Use an endmill to remove the excess material from the stock
4. Face the final part with an endmill.

This part will be made in 2.5D, which is a limitation imposed by HSMXpress. 2.5D means that your part must generally be conceptualized as a stacked series of 2D surfaces. 3D CNC machining is possible on the Mitek but requires a capable software package (such as the paid version of HSMWorks or the built-in Solidworks CAM tool).

The following are useful tutorials I have found on how to use HSMXpress in Solidworks (please add resources to this list as you discover them):

https://www.youtube.com/watch?v=gvdqKvPLDok - This is produced by the company which makes HSMXpress and is a very good overall video to understand the workflow

https://www.youtube.com/watch?v=fxO0Y9zaodc - This detailed series of videos will walk you step by step through process.

Note that you will have to modify the provided drawing to be appropriate to your cutting tools. As a general rule, the radius of curvature of any corners you make while cutting into a part should be at least 13% bigger than the endmill. This prevents the metal being cut from grabbing onto the part which can cause the part to move, excessive tool wear, and in extreme cases for the part and your tool to bind.

To avoid making soft jaws for the final profiling step, we will be using a fixture plate. A fixture plate is a plate to which the part we are manufacturing can be bolted to. This could possibly be done by simply bolting the part to the T-slots of the work table, but is not worth the risk of damaging the table. The fixture plate is made from aluminum and is considered a sacrificial part to cut in to. Here is a good general purpose overview of workholding options for CNC. Here is an excellent tutorial on the use of a fixture plate to make the outer contour of oddly shaped parts. For this course, plan to hold the fixture plate in the machine vise. The fixture plate will be provided by the course instructor.

To manage the tool change process on the Mitek, you should structure your CAM instructions as separate jobs. Each job should use only a single tool (e.g. a 1/4" endmill, or a center cutter). Each job will be exported from your CAM software as a separate file. Tool changes take place between files, allowing/requiring you to redefine the zero point (where zero on the part is, and also the length of your new tool) for the new tool manually between each step. This can be avoided by learning how to use the programmed tool library in the CNC.

Unless you have a good reason to do otherwise, you should plan for the part to be done with climb milling. This permits better tool engagement and control on the CNC. While you typically avoid climb milling on a manual mill, it is preferred on the CNC.

Once you believe you have a series of CAM steps programmed which will make the part, contact Shakeel on Slack and send him your file. If you are using HSMXpress with Solidworks, save the file as a Solidworks type file, which will preserve the CAM instructions. Shakeel will provide feedback, and if you are done, he will schedule you for the second part of the training.

Learning to Use the Mitek

The Mitek is a much more complicated machine than either of the manually operated mills. This section serves primarily as a reference for trained users and IS NOT A SUBSTITUTE FOR TRAINING. Do not try to figure out how to use the Mitek on your own, it can be EXTREMELY DANGEROUS.

The Mitek two spindle gears, a high and low speed. The low speed gear goes from 100 RPM to 400 RPM. The high speed gear goes from 401 RPM to 4000 RPM (the maximum spindle speed of the machine). Any step which requires you to switch gears will prompt you to do so without requiring a separate job, or without needing to be programmed into your CAM steps.

Before operating the Mitek, check the grease port of the spindle and add lubricant using the grease gun if appropriate. You cannot over lubricate, but you can run the spindle dry and destroy this tool.

You must manually provide coolant and lubricant to your part while it is being machined. This is done using a Koolmist water-based product from a spray bottle. Under absolutely no circumstances should you ever do anything that involves reaching near the cutting tool while it is operating, including to lubricate or clear chips. Keep an air pistol or shop vac handy if you expect to clear chips while a cutting operation is occurring.

Once you are done machining, it is imperative to clean and oil the vise and the ways with way oil. Use a shop vac to vacuum up any coolant/lubricant, remove all chips, and then dry and lubricate everything.