[davek0974]

Anyone here converted a manual Bridgeport mill to CNC?

After building my 4x4 plasma table and my bench-top mini-mill, both of which are working lovely, I WANT MORE CNC

The old Bridgeport is looking for some love but is it worth it?

It would need a ball-screw conversion kit, these are available, plus I am guessing servo drives on X, Y and Z so I have encoder display, the knee doesn't seem to get driven on the few vids i have watched so far.

On the plus side, it's already powered via a VFD and i could likely recoup some cash by selling the working power feeds, control box and new DRO i fitted last year.

Worth a look or too expensive/not good enough...



BTW I have seen the Centroid kits but I have a feeling the price is going to prevent it, I have asked for a quote anyway.

[eman5oh]

I just retrofit a Bridgeport Boss5 mill with Linux cnc, I was shopping around and was considering a manual Bridgport as well, but changed corse when I started costing out the 3 ball screws needed. I purchased a old Boss 5 mill with bad control. I went with stpepers because the mill aready had them on it and they worked. You could get a BOSS 6 or later that had DC servos if that is the route you want to take. You will if you are paitent, be able to purchase a BOSS with bad controls for likley less than the ball screws alone will cost for you conversion. That is my .02

[davek0974]

It seems to be going that way, i will be looking out for a donor machine i think.

[davek0974]

Looks like i am stuck with a standard conversion - i do not have the headroom to get a BOSS or Interact machine in the shop

The BP only fits because the head is between the roof trusses!

Will be looking into pricing up a conversion.

[vmax549]

HIYA Dave, Here teh Boss was actually shorter thatn a standard BP. The motor is mounted upside down instead of right side up making it a bit shorter. IF you look for a series 1 boss then it is about the same size as a standard BP. I did one from an old boss I had had for years on end. I used 1kw AC servos. You do NOT have to worry about super high speeds as you do NOT have the spindle speed to support it. I would look at CNCdrives for servo drives and motors. I have seen 2 BP types converted to CNC that used them and they work flawless. You may want to consider the whole package from them. UCcnc, UC400eth and their drives. It makes a really good package. The 2 mills I mentioned early are running in a job shop and are used every day. Also one was converted to a ATC mill and it works flawlessly and you could have rigid tapping as well.

For lathe work teh UC400 works very well. Encoder threading works well and there is EVEN a plugin in the works for Mach3 Turn and IT does encoder threading as well. I have seen it threading (;-).

As you have noticed a full size OPEN knee mill will allow you plenty of room to work on long/large parts. Many job shops perfere them over a small enclosed VMC where table room is very limited. NOW the only catch with a knee mill is teh short Z travel with a quill drive. You basically have 5 inches. The 2 machine I mentioned earlier are table Z driven and they work just fine as well. They are counter balanced and have plenty of Z travel.

Just a thought, (;-) TP

[davek0974]

Hiya TP, long time no chat

OK, I will look for a series 1 BOSS then before diving in.

I have also heard good things about hybrid stepper-servo motors, the people I use have some 8NM Nema34 units with drive board and cables for good price, I think easier to set up than a true servo, they have a clever digital drive that ramps current up/down according to load to help stop missed steps if it hits a tight spot.

Not worried about high speeds

Dave

[vmax549]

NOW IF you are just wanting to be a scientist and experiment with leading edge technology and all teh work and PAIN that goes with it give them a try . BUT IF you want to be a chip sligger and build lots of cool parts just get a set of standard DC servos/drives. The CNCdrives are self tuning so that takes most of that part out of the equation. With a decent knee mill servos work best because of the available torque curve across a large range of feedrates. SHURE you can go larger steppers but then you can run into midrange resonance and that requires MORE expensive drives to deal with it. Servos are best overall IF you want to be a chipslinger and make parts/gadgets.

You also may want to take OFF teh Variable speed pulley assy and just direct drive with a belt. The VS eats up about 1hp of the available spindle HP and you only have 2 to start with (;-) I setup the spindle on the High speed side at 6000 rpm max ( it was never designed to go any faster, HEAT) and then you have teh low speed side of the gearbox for MAX torque at low spindle speeds. AlSO consider a new spindle motor ,one of the New Inverter rated motors that can produce FULL torque down to almost a stop.

Also IF you cannot find a S1 boss there is a shop over here that has Kits for converting a standard BP to CNC. They sell the centroid controller BUT have a full line of Hardware for a BP to convert it to CNC. ELROD MACHINE. They have been around for a long time and know what they are doing.

(;-) TP

[eman5oh]

I am running mine with stepper right now and plan to go to servo's for smoother low-speed motion and higher precision. The original stepper that come on the BOSS mills do not like to micro step so that leaves you with .001 step size. I am looking to use the DMM Tech DYN4 drives and motors with a Mesa card to run them. To do over I think I would try a bit harder to find a BOSS with DC servo already on the mill and just replace the encoders.

[davek0974]

Nice

Ok so servos are getting the thumbs-up here. What sort of size do i look for here? 400W, 1kw, 1.5kw?

S1 Boss' seem to be very rare here, typical when you want something.

As for pulling the VS, might be easier to get a fixed pulley head

My original BP motor has been running fine on a VFD for a few years now, loves it.

[vmax549]

I have never seen a fix pulley Boss as far as I know they were all variable speed heads. Now standard BP can be either way. 1kw @1:1 drives are MORE than powerful enough so you could use as low as perhaps 400w @2:1 reduction or perhaps 750w. That would depend on what weight loads you plan to put on the table (;-)

(;-) TP

[davek0974]

Something like these maybe?

Aliexpress.com : Buy New Servo motor and driver set 2.4N.M 0.75KW 3000RPM 90ST AC Servo Motor 90ST M02430 + Matched Servo Driver from Reliable motor door suppliers on BST AUTOMATION

[mactec54]

Nice

Ok so servos are getting the thumbs-up here. What sort of size do i look for here? 400W, 1kw, 1.5kw?

S1 Boss' seem to be very rare here, typical when you want something.

As for pulling the VS, might be easier to get a fixed pulley head

My original BP motor has been running fine on a VFD for a few years now, loves it.

A Boss 1 is the first one they made, you don't want anything less than a Boss 5, if you are going with a CNC ready machine, most before the Boss 5 are warn out, so try to find one that a tech school has had

Stay with your first thoughts, with the Dmm AC servos, anything else that has been suggested does not compare, 1Kw would be ridiculous on one of these machines, I have built more than 30 of these Boss type machines, and 750w works perfect at 1:1 the standard gear ratio of the Boss 5, I have changed some of the Z axes to 2:1 on some of the Boss 5 machines, a Boos 6 already has a 2:1 ratio on all axes

There is also nothing wrong doing a manual machine, Hiwin Ballscrews Kit, is the best choice for these machines, start with just converting the X & Y axes, then you can make the Z axes mounting plates Etc

[davek0974]

Thanks Mactec,

The ballscrews are the hardest part - there are no UK suppliers of kits, I would want a kit as messing around with the dog-bone mount is not something I would want to do, this would mean finding an import source, have you any links to the HiWin stuff??

I will also need some end plates as I want to get rid of the old 6F power feeds I have on X&Y.

The main restriction on ANY donor machine is the height - this cannot be any taller than a standard BR2J2 manual machine, maybe 2-3" max then it would not fit in the shop

I was guessing on 2:1 reductions for servo drive, I cant see much point in blistering rapids on an old machine.

[mactec54]

Thanks Mactec,

The ballscrews are the hardest part - there are no UK suppliers of kits, I would want a kit as messing around with the dog-bone mount is not something I would want to do, this would mean finding an import source, have you any links to the HiWin stuff??

I will also need some end plates as I want to get rid of the old 6F power feeds I have on X&Y.

The main restriction on ANY donor machine is the height - this cannot be any taller than a standard BR2J2 manual machine, maybe 2-3" max then it would not fit in the shop

I was guessing on 2:1 reductions for servo drive, I cant see much point in blistering rapids on an old machine.

Here is a Kit on Ebay these are a C5 grade Ground Ballscrew which you don't want any less than a C5 Grade, also they are made for each Bridgeport model so these may be the wrong length for you machine

A UK Ballscrew supplier as well

Lead screw and Ball Screws Moore-international.co.uk

Bridgeport Knee Mill ballscrew Set 12" x 48" w Yoke Precision Ground New | eBay

[davek0974]

Thanks for that, great info, price is good too.

Will contact the UK one on Monday and see what they offer.

[davek0974]

So far the project is heading towards...

Converting my manual machine,
Using CSMIO/A controller,
750w servo motors with 3:1 reduction

I think 3:1 is ok here as the old girl won't like massive rapids, it increases torque and increases resolution. Figures look like 0.0006mm/line resolution which is silly for an old BP
With 5mm ballscrews, 3000rpm motors and 3:1 thats 5000mm/min rapids possible.

This package also means i get real-time position display in Mach3 so i can remove the DRO on the machine and sell that to recoup some cash, along with the working but redundant 6F power-feeds.

[mactec54]

So far the project is heading towards...

Converting my manual machine,
Using CSMIO/A controller,
750w servo motors with 3:1 reduction

I think 3:1 is ok here as the old girl won't like massive rapids, it increases torque and increases resolution. Figures look like 0.0006mm/line resolution which is silly for an old BP
With 5mm ballscrews, 3000rpm motors and 3:1 thats 5000mm/min rapids possible.

This package also means i get real-time position display in Mach3 so i can remove the DRO on the machine and sell that to recoup some cash, along with the working but redundant 6F power-feeds.

Not silly the Bridgeports I used to build, would hold .0001" cutting parts, or interpolating holes

I tell everyone the machine Resolution is only part of what the benefits are, with using a High Resolution Encoder, the smoothness that each axes run is the most important of any machine so the higher the Resolution the better it gets, it's not silly for any machine to use high Resolution Encoders, Fanuc, have them up to 32 million Per Rev , standard on a lot of machines now days is just over 1 million Per Rev or 20Bit

[davek0974]

I was meaning the figure of 0.0006mm as silly on a machine as flexible as a Bridgeport, you only have to look at her to make the DRO move on it

No slight on the BP though, I love my one and she has done some ridiculous size jobs over the years.

I was looking at the Flashcut CNC conversion video on the 'tube - they seem to use 1.8kW motors with 2:1 - seems a bit overkill ?
I need to get this right so is 750W and 3:1 a good size?

[mactec54]

I was meaning the figure of 0.0006mm as silly on a machine as flexible as a Bridgeport, you only have to look at her to make the DRO move on it

No slight on the BP though, I love my one and she has done some ridiculous size jobs over the years.

I was looking at the Flashcut CNC conversion video on the 'tube - they seem to use 1.8kW motors with 2:1 - seems a bit overkill ?
I need to get this right so is 750W and 3:1 a good size?

I have 750w on one right now and they are 1:1 they work perfect and very smooth, I only have the low 48V volt Dmm Drives, so don't get the max RPM from the motors, that you will get with the 230v Drives

You don't want to go anymore than 2:1 for the drive ratio there is no point, and no real benefit, to have more torque, and resolution, which you have plenty of for this machine

Once you put the Ballscrews in your machine and adjust the Gibs correctly it won't move around very much, when your Gibs are correctly adjusted to .0005 there is very little movement from this part when machining

Flashcut have a very good control, but forget there hardware package though

There are many controls that will work well for you I have tried/tested most

Mach3
UCNC
Eding
PlanetCNC

[davek0974]

Thanks 2:1 then

Z axis...

It looks like I have four options here...

1 - Drive the Quill direct from the bolt point where the depth gauge mounts at the front.
2 - Drive the manual lever shaft on the right side
3 - Drive the power-feed clutch shaft on the left side
4 - Drive the knee lift

Points -
Option 1 seems to be the most common but adds a lot of bulk to the front of the head and costs a little Z axis travel.

Options 2 & 3 are similar, both will suffer from the rack backlash but option 3 is the neatest one, backlash can be reduced with the clock-spring.

Option 4 is a contender I think, it gives a massive 300mm Z travel, but suffers from stickiness and has backlash in the bevel gears. The force is reasonable - I measured my one and if my figures are correct, it needs approx 1Nm to lift the knee based on the handle length of 160mm and 6kg force on that handle 6kg / (1000/160) = 0.96Nm. The backlash is a factor but the Z is usually used to plunge or position - both of these are done in the positive direction so maybe backlash does not matter here?

Thoughts?