Trying to cut steel on Homemade Milling Machine

[engineer steve]

Your mill looks like a regular drill press with a 30 taper. A fixed head and a standard spindle pull down as nearly all drill presses have.
Your 2 main problems are not your x y table or motor HP. The XY table can usually be tightened up even though it was made for a drill press.
Your ER collet adapter is way too long placing the end mill very far from the bottom quill bearing. Not sure if you can even install a larger diameter spindle in the quill.
From the video it looked like you were taking a fairly deep cut these machines don't do well with deep cuts because the head has a short distance between the bottom and the top spindle bearings, also the column does not have the mass to prevent flex.
If you will focus on limiting the depth of cut per pass and always feed into the cut, get some tooling to place the end mill closer to the bottom of the spindle you should notice better results. It will never be able to make large deep cuts, but even a 3 HP a J head Bridgeport pattern mill has its limitations as well

Yeah the cut was relatively deep but I wanted to test is the rough way. As for the spindle, I want to replace the entire quill and spindle assembly with a much bigger quill and a standard milling taper, as I said. Besides the spindle I might remake the head just like you see on the cheap milling machines with dovetails and rack and pinion (maybe making a quill somewhat obsolete ?). Thanks for the feedback!

[wizard69]

Unless you enjoy the process and experimentation that modifyiing drill presses involves, I'd suggest that modifying this machine will be a waste of time. Like "KustomebyKent" above I've been down this road, in one case because I don't have a mill and needed to get something done. In a nut shell it never works out well and can actually be dangerous if you don't have a draw bar in the spindle. A lot of your issues will start with the basic frame of the machine which as has been noted will flex significantly. There is not good way to rectify that.

Now I'm not saying abandon the DIY route, being a DIY type person my self that is why I'm here. From my perspective you will be far better off designing your own machine and building it from the ground up. Here are some suggestions that you might want to consider:
1. Consider profile rail for linear motion. In a modest home shop they should be easier to do than a cobbled together plain bearing (box or dovetails). Yes it adds expense but it also simplifies what you need tooling wise to get to an end result.
2. To go along with the linear bearings, aluminum tooling plate or ground steel plate can save you a lot of grief for some parts of the machine. Again the assumption here is that your home shop does not have large scale machining capabilities.
3. The vertical column and the base it is bolted to is critical to the machines ultimate machining capabilities. The higher your expectations the more robust these need to be. Expectations are everything here, People buy and use Sherline and Taig tools and are perfectly happy with them (some even CNC them). However most of use expect a bit more, the trick is to figure out how much more you need and to design for it.
4. The need for a stiff vertical column in most cases dictates use of steel tubing in DIY designs. This means it is really handy to have a welder or a friend with one. It might be possible to come up with a weld free design but butting something as simple as a flange on the end of a tube is dramatically easier via welding. On the flip side, understanding where to avoid welding, due to distortion, is also important.
5. One interesting reality is that CNC'ing a small machine can actually make a lot of sense as you can get the machine to operate in a repetitive manner respecting the machines mechanical capability. In other words CNC allows you to use smaller tools and chip loads to achieve a result that does not become tedious if attempted manually. An example might be cutting a slot, if it takes a CNC a half hour and many passes to get to a result, it isn't a problem.
6 Now that you have this "mill" you have enabled yourself to build a better mill. So don't knock this machine you have, just work within its capability to get you do a more robust machine.
7. Machining requires a wide range of spindle speeds. The easier it is to achieve speed changes the better but variable speed motors are not a complete solution. You really need to have a the ability to achieve a significant reduction ratio. This might be in the range of 60 to a 100 to 1 if you are running a 3400 RPM motor. Torque is an issue but some cutting operations simply need lower speeds for the tool or the part to survive. One common example is running a large hole saw or Forstner bit in wood, you need to keep speeds low to prevent heat build up burning the wood or in some cases pulling temper from a cutter. For metals, Stainless is a good example of where you often need spindles speeds well below half used for mild steel to avoid work hardening and the evils there. Sometimes you need the torque too, I'm just trying to point out that a machine can really benefit from a transmission that offers a significant speed reduction in some form. In low end machines that usually means multi reduction belt drives.

I might add that a lot of modern drill presses do not offer the speed reductions that you may need. This is a pet peeve of mine.

Yeah the cut was relatively deep but I wanted to test is the rough way. As for the spindle, I want to replace the entire quill and spindle assembly with a much bigger quill and a standard milling taper, as I said. Besides the spindle I might remake the head just like you see on the cheap milling machines with dovetails and rack and pinion (maybe making a quill somewhat obsolete ?). Thanks for the feedback!

Some other things related to the above;

A quill is extremely useful on a Mill (just look at the common Bridgeport) but it is an implementation headache on a DIY mill. This is again where CNC or motor driven feeds, can be a big win on a DIY mill, a motorized linear axis can in many cases make up for the lack of a quill, Depending upon how deep you go down the rabbit hole you can do linear feeds that are in sync with the spindle. Even if you don't go that deep it is often fairly easy to get a decent feed rate manually setting the speed.

In other words they quill can go away no problem but you really will want a way to feed the Z axis precisely. You don't even need to build this capability in at first, just make the mill so that it is easy to add later.

As for the spindle itself a standard taper implies pretty big bearings and thus a fairly large machine right from the start. I'd suggest looking at just how large an 40 taper spindle is in cartridge form. Even a 30 taper can be large. In all honestly I'd consider a smallish taper until you have a more robust shop. R8 or even an ER spindle would be good enough in a home built machine of this class. The exception would be if you have the equipment or access to equipment, to build up a very robust machine. This quickly can become the difference between a machine that weighs a few hundred pounds assembled and one that weighs several thousand pounds assembled. I can not see a reason to built a 40 taper machine that can't take advantage of the taper to even a limited degree.

I'm not a big fan of dovetails on DIY unless you have the tools to pull it off. As for Rack and pinion I really believe that a lead screw is better even if it might be more complicated to implement. The primary issue with rack and pinion is backlash and how you deal with it. Leadscrews have their issues too but I just see the implementation as being easier.

Before going too far I'd take a look at TAIG Tools and their Micro Mill and then look at all the DIY mills on the internet and try to come up with a size that makes sense to you. Then take the time to figure out how you make a mill of that size as stiff as possible. If you are looking for a bench top machine also figure out how much weight the bench can support. You can do a decent bench top mill but I really doubt it will be much lighter than 300 pounds to get decent results and likely a bit more.

Lastly what ever you build operate it within its capabilities!!!! ANY mill can be operated beyond its capability leading to finish or dimensional failures or in some cases a broken machine.