BF20/G0704 Spindle Belt Drive Advice/Info Request

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joco-nz

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Hello everyone. This request is for both myself and a mate. We both have BF20 or equivalent machine that has been converted to CNC for hobby use and in that setup are quite effective. We are now looking to push them forward again with a belt drive upgrade from the current geared system.

We believe Poly-v belts (other names being "micro V belts" and "ribbed belts") are the way to go and from what I have read the J profile seems to be right size as it will cover the rpm needs and horse power need (i.e. rpm on the small pulley up to around 5000 to 6000 rpm and a power rating of 750W on the spindle.

What I am hoping members can help with is as follows:
[1] Is the J belt profile appropriate? If not what would be a better choice and why.

[2] Help with the specs we will need for the belt pulleys. We understand that the Precision Mathews PM25 is a poly-v belt drive based machine of the same class as the BF20 or G0704. If anyone is able to supply specs (dimensions/drawings) on those pulleys it would really jump start things.

[3] with reference to #2 and the PM25 what belt spec/number is used.

I realise these questions might be a bit PM25 centric. That is because this seems to be one of the best examples of commercially available machine that comes stock with a poly-v belt drive.
If someone has an alternative BF20/G0704 type machine with stock poly-v d drive or have done it fully custom from their own design on that class of machine which has been successful and they are prepared to share, that too would be absolutely invaluable.

Hopefully the combined wisdom and experience of the group can boost us on our next stage in upgrading these wee machines.

Looking forward to the responses and shared experiences. Equally if anyone is interested in or wants to see what we have done and how we did it (plenty of other well documented examples out there) I'm more than happy to post info, plans, photos.

Cheers,
James.
 

michelko

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Hi James ,
greetings from Germany. I own a Optimum BF20 that is converted to cnc. A real anoying Thing is the gera Setup with the noise it makes.
After the DC Motor went bad i converted the mil to an 0,55 kW AC Motor with vfd and a 2 Speed Polybelt transmission.
Now the noise is nearly away, a pleasure to work with.
Here are some pics.
20200524_105558.jpg
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20200524_105539.jpg


If you have some special questions feel free to ask.

Regards Michael
 

RonGinger

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I have the G0704 version. There is only a very small place to connect the new pulleys to. How did you make the connection to add the thicker pulleys?

thanks,
 

michelko

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Hi
i made an Adapter from free turning steal glued with Loctite into the spindle gear with additional worm screws for safety.
The pulley is then mounted with allen head screws
20180211_180517.jpg
screws to the adapter.
20180211_180506.jpg

20180211_180522.jpg

20180211_180627.jpg


With the adapter glued in place i used the Mill as an lathe to get the right outer diameter and runout. Powered the spindle with a cordless drill.

Regards Michael
 

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joco-nz

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Michael,

Super helpful! Looing at that adaptor I take it that you are pushing/glueing it into this fitting? Nice idea in doing the mill-athe like thing to get the fiting running concentric. Where you out by much initially?
Also did you make the pulleys yourself or are they stock items hou were able to purchase and tweak the holes as needed?
1590367334778.png
 

joco-nz

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Also, any advice on how you took this top bit off.? The part with the magnets in it.

bf20-spindle-top - 1.jpeg
 

michelko

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Hi you can just pry it of with some big screw drivers. Its just a slight press fit.
I turned the pulleys on my lathe.
I cant remeber the exact number of runout but that gear part had some. Maybe 1/10 mm

Regards Michael
 

CFLBob

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I also have the G0704 version, converted to CNC and have a couple of questions.

First, did you set up your motor to be controlled under CNC with the motor start/stop and RPM commands? Second, I've been thinking of changing out my motor to allow threading under CNC. Can your system do this?

Finally, did you increase spindle speeds? In a few frames of the video, I think I see the mill's display reading over 3700, and there's that other display (the red LEDs at 0:45) saying 2646.

Thanks
 

michelko

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Yes the Motor is controlled by the cnc Computer. On the breakoutboard is an relay that starts the Motor and 0-10v Signal is generated for the Speed.
The Optimum RPM Display is out of function because i havn´t fitted the Magnets. the red led Display is the rpm of the Motor displayed on the vfd.
At the high gear thr atio is 1:1 so i have a max spindle rpm of ca. 2800rpm.
If necesary one can bump up the vfd output to 60 or 70 Hz for some higher rpm.
 

Wizard69

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Hi James ,
>>>snipped
If you have some special questions feel free to ask.

Regards Michael
That is a nice looking upgrade!

Do you happen to know your ratios for high and low?

I'm not really sure why the builders of these machines even bother with gears when the mills aren't not suitable for high torque milling in the first place. Belt drives would even be cheaper.
 

Wizard69

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Hello everyone. This request is for both myself and a mate. We both have BF20 or equivalent machine that has been converted to CNC for hobby use and in that setup are quite effective. We are now looking to push them forward again with a belt drive upgrade from the current geared system.

We believe Poly-v belts (other names being "micro V belts" and "ribbed belts") are the way to go and from what I have read the J profile seems to be right size as it will cover the rpm needs and horse power need (i.e. rpm on the small pulley up to around 5000 to 6000 rpm and a power rating of 750W on the spindle.
Poly V or similar profiles are the way to go.
What I am hoping members can help with is as follows:
[1] Is the J belt profile appropriate? If not what would be a better choice and why.
J should work, but it is advisable to go through the engineering calculations to make sure. I'm attaching one design guide, not the one I was hoping to find but it should help. Note that on page 190 you can figure out the horse power per rib.depending upon the power you want to deliver you may find yourself needing a 5 or 6 rib belt. If you keep your pulley diameters up you should be able to hit 1HP, running a speed reduction.
[2] Help with the specs we will need for the belt pulleys. We understand that the Precision Mathews PM25 is a poly-v belt drive based machine of the same class as the BF20 or G0704. If anyone is able to supply specs (dimensions/drawings) on those pulleys it would really jump start things.
I don't have a PM yet but the online manual indicates a: "406PJ5" belt. The pulleys are: "WMD20VH-02-00612-step spindle pulley" & WMD20VB-02-004A12-step motor pulley"
[3] with reference to #2 and the PM25 what belt spec/number is used.

I realise these questions might be a bit PM25 centric. That is because this seems to be one of the best examples of commercially available machine that comes stock with a poly-v belt drive.
Yeah I'm not sur why more machines haven't gone this route. It actually should be cheaper for he manufacture. Part of the problem may be due to the ability to deliver power at lower speeds but that isn't the way most of these machines are used. That might be better said as torque at low speed.
If someone has an alternative BF20/G0704 type machine with stock poly-v d drive or have done it fully custom from their own design on that class of machine which has been successful and they are prepared to share, that too would be absolutely invaluable.
Haven't gone there yet.
Hopefully the combined wisdom and experience of the group can boost us on our next stage in upgrading these wee machines.

Looking forward to the responses and shared experiences. Equally if anyone is interested in or wants to see what we have done and how we did it (plenty of other well documented examples out there) I'm more than happy to post info, plans, photos.

Cheers,
James.
If I was about to ugrade or even build a machine of any type, I'd certianly be looking at poly V type belts for power transmission. The biggest problem on these mills is getting enough of a speed differential between the two belt positions to make a real difference. I would almost prefer a mechanical modificantion to allow a greater speed reduction on the low speed option. That gets tricky though because you need to keep an eye on what power transmission is possible within the mechanical envelope.

Unfortunately I did not find the Gates manual I was looking for which went into the engineering calculation in depth. I haven't looked into their design ware. However I've found a German supplier that has a far better engineering manual and attached that.

Ultimately you are compromised by the mechanics and thus will likley have to accept hat you will not get as much power to the tool at low speeds that you might hope for. Well if my quick review of the charts is accurate. The charts also imply industrial duty so that is another consideration.

Best of luck!
:):):)
 

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Foketry

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This is the solution that I applied to my Chinese milling machine (G0704) converted by myself through DC motors in CNC
I kept the 1.5 Kw electric motor and the original transmission for steel and cast iron and applied a 2.2Kw air cooled spindle motor whit inverter on the left side, 20,000 rpm for aluminum milling.

IMG_0512.JPG
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IMG_0515.JPG
 

CFLBob

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I see your control panel closest to the high speed motor says Drilling/Milling Stop Tapping.

Is that done with a tapping head, like Tapmatic that reverses itself or hard tapping (I think that's what it's called) where the tap is held directly by the motor and it advances and reverses itself? Can you comment on how you tap?

Thanks!
 

Foketry

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I see your control panel closest to the high speed motor says Drilling/Milling Stop Tapping.

Is that done with a tapping head, like Tapmatic that reverses itself or hard tapping (I think that's what it's called) where the tap is held directly by the motor and it advances and reverses itself? Can you comment on how you tap?

Thanks!
My milling machine can automatically reverse when it reaches a certain depth, previously set by an adjustment wheel ( vertical graduated scale ) or by manually pressing the reverse button.
For a blind hole I normally use the manual function. when the tap reaches the bottom, he slips into collet and I press the reverse button .
 

joco-nz

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Some great info here and ingenuity.

I’m busy modelling out how I will do this. Following Michael’s example and the detail from his german site posts (thank goodness for google translate). This is where I currently have the design thinking.
51466384-B3C3-4E4B-8419-E3BC9CAC7479.png
 

tmibbs89

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I stumbled across this thread as I am finishing up a CNC conversion on a PM25MV, and wanted to upgrade my spindle. I would love to keep my poly-v belt, but I can not for the life of me find any resellers of polly-v pulleys in the US. Is there some source for them I am trying to keep a simple 1:1 ration on the pulleys as I am looking to upgrade to this BLDC, which should be plenty of speed for my needs. I just cannot for the life of me find a place to get a pulley. Anyone have any suggestions?
 

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