Bridgeport Manual to CNC conversion...

[m_c]

The first thing that springs to mind, is how much play is in the quill?

By bolting onto the quill the way you have, any play in the quill will be greatly magnified at the second spindle, so it's probably not taken much extra wear to go from tolerable to a problem.

Creating a new Z-axis assembly sounds like the best long term solution.

[Davek0974]

Yes, I was working through this on the drive to work this morning ;)

There will be play, must be or it would seize, plus being umpty years old i guess there will be a measurable amount.

The setup is perfect on the 2mm tools or engraving etc so it seems somewhere between 2mm and 5mm tooling is a point where cutter force and reaction come into play and bite me in the arse.

I am leaning towards a fully custom Z axis now, this brings about its own set of issues of course -

Will have to move machine away from rear wall,
..Can't move machine away from rear wall as the head hits the roof truss,
....Will have to radically modify roof truss to make clearance,
The list goes on - sometimes i hate my garage shop.

Next is - steel or aluminium build??

I am visioning it as being just a larger version of the Z axis on my mini-mill so two flat plates with rails and a screw sandwiched between, servo motor to drive and a toothed belt?

It does not need massive rails as the biggest tool is likely to be 5-6mm max so probably the same 20mm HiWin and a 1605 screw, maybe use stuff with a pre-load this time??

The hard part is working out the connection to the rear of the ram and where to put strengthening trusses/plates etc - the rear of a BP ram is a spigot maybe 50mm tall, 110mm wide and 100mm deep with a 20mm hole central - that is all i have to mount off of.

So, something like 25mm tooling plate all round or go steel and weld etc where possible.??

[m_c]

My thought would be to weld the BP side, as it gives you more flexibility in terms of bracing/reinforcing. You would ideally need to stress relief it before doing the final machining for the rails, to minimise any long term stability issues.

[Davek0974]

So, welded interconnect plate, relieve, then machine square etc.

Then build the motion parts in Alu ?

[Davek0974]

Hmmm,

Just been playing speeds & feeds for my single flute 5mm tool...

Manufacturer specs...
12k Rpm
2.5m DOC
1800mm/min feed - insane i think?

My previous settings...
12k rpm
2.5mm DOC
900-1000mm/min feed

F&S Calculator recomendations...
12k rpm
1.8mm DOC
280mm/min feed - much lower ?

Maybe these lighter settings will be better?

Its only the bigger tool that has issues so does seem to be a stress problem, I will also attach a bungee cord to the head to try and remove any rotational slack in the quill.

[Davek0974]

Ok, did some tests, first was to measure slack in the z axis at the adaptor in line with the high speed spindle - I have 0.02mm vertical (with reasonable force) and 0.15mm rotational around the quill - no doubt the source of my trouble.

Left cuts in the first picture below was at the feed recommended by my S&F calculator shown in the last post, 2 passes of 1.25mm ea, top cut is with me applying pressure to the motor while cutting to remove slack, the lower cut is with it running free as normal.

Both cuts look fine, no burr on the lip and pretty much perfect.

The right cuts in the first pic show results of a single 2.5mm DOC pass, same feed rate, again with hand pressure on the top pass and free on the lower.

Both cuts are acceptable this time but they show signs of vibration on the bottom surface - this is not an issue here as this tool is a roughing tool and will cut right through on these parts.

the second pic is just a closer view of the vibration on the second cuts.

Seems I just have to back off on the fast pedal a bit and let her do her thing, plus fit a bungee cord to remove the slop.

[redtom99]

Ok, did some tests, first was to measure slack in the z axis at the adaptor in line with the high speed spindle - I have 0.02mm vertical (with reasonable force) and 0.15mm rotational around the quill - no doubt the source of my trouble.

Left cuts in the first picture below was at the feed recommended by my S&F calculator shown in the last post, 2 passes of 1.25mm ea, top cut is with me applying pressure to the motor while cutting to remove slack, the lower cut is with it running free as normal.

Both cuts look fine, no burr on the lip and pretty much perfect.

The right cuts in the first pic show results of a single 2.5mm DOC pass, same feed rate, again with hand pressure on the top pass and free on the lower.

Both cuts are acceptable this time but they show signs of vibration on the bottom surface - this is not an issue here as this tool is a roughing tool and will cut right through on these parts.

the second pic is just a closer view of the vibration on the second cuts.

Seems I just have to back off on the fast pedal a bit and let her do her thing, plus fit a bungee cord to remove the slop.