DIY milling machine

Hi,

I want to build a milling machine. Just for fun. I have no experience so I was looking for something simple. I bought a Bosch PBD 40 bench drill, a milling table and this precision vise.
The milling table was full of rust, had a lot of play and was covered in a bad smelling grease. I cleaned it and painted. Fortunately it was possible to adjust it to remove the play. I stacked everything together like this:

The table is moving smooth but unfortunately I underestimated the rigidity required to mill metal. I have a 5mm carbide mill and I was able to cut the top of a nut. But I think I was lucky that the mill didn't snap. There were a lot of vibrations. This is the result:

I like the table so I will keep it but I want to replace the column drill. So I'm evaluating different options for building a more solid frame. I'm open to any option, from steel to concrete.

Buna Ziua, and welcome to the Forum, Andrei.

I have to admire your ambition to want to build a mill from scratch - but I fear it is not an easy job. You will definitely need a much more rigid arrangement than most pillar drills can provide.

I have sent you a private email - look at the envelope in the green line at the top of the page when you are logged in.

Could you tell us what type of work you intend to do, and this dictates the type of machine you need?

Regards, An

Hi An,

I don't have any type of work in mind. I just find it interesting to build one. I have some vague requirements like to be able to move it alone, up to 10cm of vertical movement and should work with mills up to 7-8mm. Cutting speed is not an important factor. But I would like to be as precise and vibration free as possible.
My current idea is to make a frame from half inch thick metal plates. There are plasma cutting companies in my area and I can weld reasonably well. But I have to check the precision of this cutting method. Because they usually cut metal sheets for fences...

Also I found this in the local used market, a kind of milling head:

This thing has an ISO 50 cone and I estimate to weight around 60kg. It is larger than what I was planning but the price is ok and I'm wondering how difficult could be to use it. Maybe to replace that teeth wheel with a pulley for a belt?

Buna Ziua,

Your setup is not rigid enough for milling steel. But if you use a smaller end mill the cutting forces will be less. This will give better results. Take your time because smaller end mills are brittal.

For a 3 mm HSS end mill in mild steel you can run 3400 RPM. Make sure you make (thin) chips. If you make "dust" you are feeding to slow and this will quickly dull your end mill. If you feed to fast, you make thicker chips but also risk breaking the end mill.

There is no need to start learning milling using expensive end mills. When you no longer break end mills, it is time to move up to a better and more expensive end mill.

with a home made setup for milling steel you really need weight/mass of 100KG plus to absorb the cutting forces

and in milling world, 100KG is a lightweight

Edited By Ady1 on 07/02/2023 23:32:03

The table is moving horizontally over a dovetail?

I continued to think about the options and currently I have two dilemmas. First, what spindle to use. The one that I posted above I don't like it. Seems difficult to adapt a pulley to it. And also I don't know in what condition it is. From my research I concluded that there are two widely available options. One is a combination of air or water cooled high RPM motor that include ER collet:

The second option is only a large cast iron block with an BT30 tool holder:

This one is limited to lower RPM. But I don't need high speed if I'm not in a hurry, right? The green one looks more solid to me. But the first is easier to use.

The second dilemma is the vertical movement. I'm thinking to use a solid vertical tube. Something > 4" in diameter and very thick walls. Similar to this home made contraption:

But I'm not sure how to make that piece that slides up/down over the column. Maybe another pipe with interior diameter just a little larger than the column diameter? I could slotted it to be able to clamp it over the column before milling.

I simply repurposed already capable kit, a Drummond M lathe with a good headstock and a 40 kg milling table so the hard work of decent accuracy and stability was already there, I simply bolted them together

and it still shakes if you take too big a bite, using only 6mm cutters mainly

Only a multi skilled machinist with good resources could make a decent mill from scratch in my opinion, because it needs to be very accurate when it does work, sub 0.5mm across the entire working plane, sub 0.1mm preferred, up/down left/right otherwise it's been a waste of effort

The table is moving horizontally over a dovetail?

The table is bolted "immovably" to the cross slide but can move up and down the lathe bed with the leadscrew

It's actually fabulous for big woodwork jobs because all the mess drops down out of the work zone

Edited By Ady1 on 10/02/2023 23:35:52

Before you go too much further, work out what RPM will be required for the materials / tools you want to use (from published cutting speed information) - High RPM may be more of a curse than a blessing.

For example, if you want to cut steel with a 6mm diameter tool, the maximum spindle speed is ~3000 RPM for HSS and ~8000RPM for carbide. I think that both of these are below the minimum RPM for the first type of spindle.

First off, I would say "just buy a mill". If you ignore that, then I would steer you towards the second type of spindle for a mill.

I built a router type machine (CNC) with a cheap, air-cooled spindle motor, and it was nowhere near rigid enough.  After some re-engineering, it will cut aluminium (fairly happily) and steel (not so happy). It is still not very rigid and I'm in the process of making a new spindle along the lines of your second option.

Cutting test for material removal (it runs a bit happier with lighter cuts):

Good luck

Edited By Andy_G on 11/02/2023 10:01:23

...and once you start taking successful light cuts you realise that some jobs will take forever and you wish you could take heavier cuts so you can get on and do more stuff...

If you are going to do metalwork and you can afford and accommodate a chunky mill then it's actually a no-brainer to go for as-chunky-as-possible from the very start

Lathes are a lot easier because even a decent smaller lathe can do quite heavy work, but a decent smaller mill cannot do quite heavy work

Ady1 mirrors my thoughts perfectly.

I will add that building a conventional milling machine from scratch is substantially more expensive than buying one of an equivalent level of rigidity.

I've helped two friends build custom CNC mills, and even discounting the electrical and control element it's a big undertaking.

For my sins I'm working up the plans for a Horizontal Boring Mill at the moment and even the steel for the frame to hold the (repurposed) bedways comes to more than a second hand bridgeport.

This thread may be of interest.

**LINK**

If you are serious then another 'food for thought' item are these pictures & descriptions of the of the origins of the BCA jig-borer; built like the Boley & Leinen with a plain compound table it doesn't get much simpler than this.

Lathes.co.uk - BCA Jig-Borer

I would council that unless you have access to a well equiped workshop what you make will (a cost quite a bit of money and (b be a disappointment to you.

Buy an old machine and re build it, even one from a scrap yard will be a better bet than starting from scrach. Good Luck. Noel.

Everybody does I think! A pillar drill looks so much like a milling machine that one feels it ought to work after a fashion, even if only light cuts are possible.

The problem is that drills only have to deal with up/down forces, and consequently most of them resist side pressures poorly. Even big chunky pillar drills bend, vibrate, and lose their chucks. Horrible.

The only good news is that vertical milling machines have no trouble with drills. Apart from the cost, milling machines are wonderful!

Dave

Edited By SillyOldDuffer on 11/02/2023 15:51:02

It seems it is possible to use a bench drill if it has the right nose. This picture from:

**LINK**

Anything is possible right, and starting with a pretty over-built drill would obviously help... But it may not be easy or cost effective to get the performance desired.

If there's an MT spindle nose and the spindle is bored through (or can be) to accommodate a draw-bar then that gets over one of the two big issues.

You could probably even turn down and bore out a solid spindle with an external screwed or JT nose to fit an internal MT2/3 ISO20/30, or ER32 taper, provided it has enough "meat" to it.

There's also the consideration of how rigid the bearings are with respect to side-loading, most cheaper drills will use one thrust bearing at the bottom and one or more deep groove bearings further up, that will result in deflection during side loading and quickly destroy the bearings.

High-end drills sometimes use angular contact ball bearings instead which may be able to cope with milling forces depending on their arrangement in the spindle and pre-load forces.

Depending on the existing bearing seat sizes and how they're pre-loaded one could fit angular contact or taper roller bearings to improve a spindle for milling.

That leaves five issues left to to overcome:

• Rigidity of the body/table itself,
• The rigidity of the quill within the body,
• Precise z-axis adjustment,
• Secure locking of the quill to prevent z-axis creep, and
• Rigidity of mounting the x-y sub-table to the main drill table.

All solvable (for a given level of solved), but some more easily than others.

Edited By Jelly on 11/02/2023 16:47:12

Edited By Jelly on 11/02/2023 16:51:45

If you click on the link you’ll see it’s pretty much a standard Fobco Star bench drill apart from the nose and a couple of other minor bits. Nothing “over built” (whatever that means?) that I can see.

**LINK**

Something like this may well suit the OP?

The Fobco is built very solidly, out of substantial castings, and uses a very rigid spindle design, which includes a pair of angular contact bearings preloaded against each other, which is not unlike the arrangements used in many modern "hobby" milling machines.

Compared to a more modern drill press, that definitely qualifies as being over-built (as in the design and materials of construction significantly exceed the minimum required to do an acceptable job).

My experience using Fobco drills is also that the fit and finish of the quill and the bore it slides in is also unusually high by modern standards, as is the inclusion of a quill lock of the highly rigid split casting type.

As such it is actually uniquely suitable to be re-engineered as a lightweight milling machine, in a way that very few drill presses actually are.

My big drill press is an early '90s Sealey with an MT3 spindle, and is far more capable as a drill than a Fobco star is, as well as seeming like a far more substantial machine...

But in reality it's internals have been heavily value-engineered to give maximum drilling for minimum money, so it would rapidly shake itself to bits if used for milling.

OP needs to be aware that not all drills are made equal, and if he wants to go down that route he needs to examine parts diagrams or sectional drawings to understand if the construction of the spindle is suited to conversion to milling.

Edited By Jelly on 11/02/2023 20:13:03

Both Emco Unimat and Hobbymat do Milling attachments for lathes that were sold in Europe.

If you can make a good strong accurate drill then you can do 80% of a lot of milling jobs, it's a lot cheaper on the tooling too, and faster, the drill swarf can really pile up compared to a light milling cutter because you can do up to 12mm and work it hard

Then swap tooling and finish with light accurate cuts with the 5-6mm milling tool

I suppose that's a good way to test an unknown drilling machine, stick a sharp 12mm drill into the chuck and see how it does with drilling through a 20mm mild steel block. If it's a doddle then you only need to add an X-Y table to give yourself a light milling machine

One on the bay at the moment that would get me excited if I was in the market

Edited By Ady1 on 11/02/2023 23:49:00