DIY Epoxy composite gantry frame milling machine

[John McNamara]

Hi All

Its been a while since I popped in here, I am working on a new milling machine build. This not a light weight design. It has been designed to work with steel or Aluminium depending on the spindle fitted.

Alas the thread describing making i will be huge by the time it is finished so posting on multiple forums is difficult.

I have posted it at another place nearby. https://www.model-engineer.co.uk/for...?th=139042&p=1

You may find it interesting.

Regards
John

[mekanik]

Hi John
Thanks for the heads up, i have been thinking about this for some time and a couple of years ago composite guy promised some info on construction but this was never forthcoming, i will be following with interest.
Regards
Mike

[Greeny]

Thanks for the pointer.
Very interesting so far, looking forward to the rest.
Cheers

[pippin88]

John, looks like a great build.

If you don't mind sharing, where in Aus are you? I'm in Melbourne.

I'm in the early design stages of a DIY mill. Manual conversions are troublesome, and true CNC machines are either tiny or very large and not feasible in the home shop / garage.

I'm planning a steel weldment, stress relieved and machined +/- ground. This is partly because I've struggled to find clear recipes for epoxy granite and don't really want to spend months experimenting. I may use epoxy granite to fill voids and add mass.
I'm looking at doing a planer style mill - double columns, with the gantry moving up and down on the columns. This avoids the long lever arm Z axis, but is a bit more complex to align.

I have a couple of comments and questions about your build:

I really like the rail alignment cams - did you make these or buy them? They are going to be great for both alignment and increasing mounting strength of the rails.

The Z axis travel seems a bit short compared to your other travels. What sort of spindle / tool holder are you going to use?

What was the cost of the laser cut steel? Do they cost it per cm cutting length or similar? I'm interesting in getting a milling head and gantry beam laser cut. I'll probably use square hollow section for the base however.

[John McNamara]

John, looks like a great build.

If you don't mind sharing, where in Aus are you? I'm in Melbourne.

I'm in the early design stages of a DIY mill. Manual conversions are troublesome, and true CNC machines are either tiny or very large and not feasible in the home shop / garage.

I'm planning a steel weldment, stress relieved and machined +/- ground. This is partly because I've struggled to find clear recipes for epoxy granite and don't really want to spend months experimenting. I may use epoxy granite to fill voids and add mass.
I'm looking at doing a planer style mill - double columns, with the gantry moving up and down on the columns. This avoids the long lever arm Z axis, but is a bit more complex to align.

I have a couple of comments and questions about your build:

I really like the rail alignment cams - did you make these or buy them? They are going to be great for both alignment and increasing mounting strength of the rails.

The Z axis travel seems a bit short compared to your other travels. What sort of spindle / tool holder are you going to use?

What was the cost of the laser cut steel? Do they cost it per cm cutting length or similar? I'm interesting in getting a milling head and gantry beam laser cut. I'll probably use square hollow section for the base however.

Hi
I am in Melbourne 3122

John1147 at big pond .net.au

You will have to edit the address above I guess you know how.
If you email your phone number I will give you a call :)

[John McNamara]

Hi
Most laser cutters provide the mild steel and cutting at a quoted price. Many will also have Stainless and Aluminium Etc.
It is not possible to work out the cost on the basis of so much a millimeter.

The main thing is to provide properly drawn 2D files, usually DXF files. The part outline must not have any breaks or overlapping lines, All holes must also be closed. (And nothing else in the file) Each part should have its own file. Don't try to nest the parts yourself in a big file.

Laser cutters are pretty busy businesses, If you provide good files you will be charged as a professional. If you cant provide files some will draw the parts for you, be prepared for a shock when they quote to do this.

Just email your requirements and the file set in a Zip file and most will reply with a quote in a day or two. (A separate zip file should be used for each material type and thickness. this avoids confusion) It is OK to have a short discussion when starting with them asking if they have any special requirements.

I really like the rail alignment cams - did you make these or buy them? They are going to be great for both alignment and increasing mounting strength of the rails.
[
I had them laser cut from 4mm steel they cost about 50c each the laser cutter provided the material

The Z axis travel seems a bit short compared to your other travels. What sort of spindle / tool holder are you going to use?

I drew in an Asian high speed spindle fine for Aluminium Brass and plastics and fairly low cost. I also plan to build a 30 or 40 taper spindle, Possibly using the high speed 2000 rpm spindle with a 4 to one reduction belt drive. I also have a large Manual V Mill, It is easy to make the Z axis taller I decided not to as this machine will be used for smaller parts. Shorter = less deflection

What was the cost of the laser cut steel? Do they cost it per cm cutting length or similar? I'm interesting in getting a milling head and gantry beam laser cut. I'll probably use square hollow section for the base however.
Laser cutting cost of the machine parts was about $500 including material plus the molds that cost more I am sharing the cost of the molds. 160+ part files is a lot quite a few of the parts were in multiples. looking at it that way the cost per part is modest. FWIW the cost per kg of parts was AUD $3.85 All up inc GST/VAT. I would not try to use that figure it will depend on the mix of parts, OK I guess as a ballpark.

[pippin88]

Thanks for the update John. Nice results.

So, do you reckon it's best:

a) To get ground stock (can be bought ground, but suspect $$$), predrill (most) holes and cast against surface plate as you have done

or

b) Use mild steel bar stock, cast in standard mold, not requiring surface plate, and pay someone with a big cnc mill to quickly machine the steel and drill the holes?

[John McNamara]

Hi Pippin in answer to your questions A and B.

Question A. “To get ground stock (can be bought ground, but suspect $$$), predrill (most) holes and cast against surface plate as you have done”

I considered precision ground stock and phoned around to locate a source, it was available at a cost, quite a lot actually; however the supplier would not guarantee flatness on longer lengths. They would provide a tolerance for constant thickness but not flatness, however for this project only one side has to be flat the other side is buried in the casting.

Laser cutting precision ground stock which is normally a water or oil hardening carbon steel is likely to make any hole or laser cut edge very hard. Also my laser cutter charges extra for precise positioning small pieces of material, they prefer to work with large plates. This hardening also occurs to a small extent with mild steel, making it hard going for high speed steel tools however I did not have a problem with HSS on the steel supplied by the laser cutter.

If I was able to locate precision ground stock with a guaranteed flatness it would have to be machined to size and the 16mm holes for the cam pins would have to be drilled. These holes do not have to be located to high accuracy so marking out and centre punching in the normal way would be fine. The cams will compensate for any small errors.

The 16mm thick standard mild steel plate supplied by the laser cutter has a reasonable surface finish free of the normal flaky scale you get on black bar stock, there is a black oxide coating and some mill marks. After cutting it is not flat there was heat distortion, bowing of the 16mm axis in particular. I mechanically straightened the pieces and then sent them to a firm with a surface grinder. This was not a success as they did not completely flatten then pieces. I suspect their operator was not up to the job. The big enemy is the magnetic chuck. Grinding long pieces requires packing the work so the chuck does not pull any bowing down before grinding a side then, then turning it over and repeating the process for the other side. This process may have to be repeated several times until any stresses are relieved and the piece will lay flat on the surface table. Even better would be to have the part stress relieved professionally another cost.

In the end I hand lapped the errors left by the surface grinder. As the post above shows there were some residual errors.
I have been working on them with the lap and now the maximum error is .001” over 800mm testing the part on the surface plate with an indicator. I am confident I can get that down to a tenth or so, however just turning the part 90 degrees would probably change that, gravity is a universal force. I guess I could set the part up on its airy point’s that would possibly reduce the measurement error however temperature is also a variable. My workshop has a skylight. We happened to have a hot day yesterday a high of 33 today the high was 20. As expected my error measurements changed with the sun shining on the part; the top face was heated and the face bowed up. Digging the depths of high accuracy is an interesting challenge.

Question B. “Use mild steel bar stock, cast in standard mold, not requiring surface plate, and pay someone with a big cnc mill to quickly machine the steel and drill the holes?”

That will work no problem, apart from finding a contractor that has a CNC machine and equipment that can handle large heavy parts and cost.

It was tempting me to take that option, were it not for the desire to to find out what is possible using a surface plate, small lathe and basic tools. The laser cut mold is optional it could be made of MDF for one time use. The machine does use laser cut parts, they could also be made by hand a large time cost. If I manage to make a workable machine and demonstrate a method that worked I hope others will maybe create their own designs and contribute improvements to the methods I have used for this machine.

[John McNamara]

Hi All

I just completed the columns for the mill next is the base, an exciting step as for the first time the frame of the machine can be tested.

I have a full write up here.
https://www.model-engineer.co.uk/for...?th=139042&p=2



Regards
John

[pippin88]

Fantastic work!!

My mill looks like it will have to wait a good 18 months unfortunately. I will have to live vicariously and get the benefit of the what you learn.