distortion of steel when machining
I have a large gates pulley that i am using for the transmission of my servo driven bt30. It is an 80t 5mgt mounted on the shaft of my 1kw servo. It works but this pulley has a huge amount of inertia to it and greatly limits how fast i can accelerate my spindle without faulting the servo, almost an inch thick and 5 inch diameter solid steel. Since i am only pushing a few hp peak at the most, this pulley does not need to be that beefy and i could about cut the inertia of my whole system in half by hogging out the center of this pulley and replacing it with a spoked aluminum hub. Question is, how much material can i remove before the pulley starts distorting and going out of round? Im not sure what exactly the process is for making these pulleys or what the material is. I would think the rough shape is probably cast and then post machined so probably somewhat stable as i remove material but i just dont know. Do i need to worry much about distortion as i machine it?
Re: distortion of steel when machining
Quote:
Originally Posted by
QuinnSjoblom
I have a large gates pulley that i am using for the transmission of my servo driven bt30. It is an 80t 5mgt mounted on the shaft of my 1kw servo. It works but this pulley has a huge amount of inertia to it and greatly limits how fast i can accelerate my spindle without faulting the servo, almost an inch thick and 5 inch diameter solid steel. Since i am only pushing a few hp peak at the most, this pulley does not need to be that beefy and i could about cut the inertia of my whole system in half by hogging out the center of this pulley and replacing it with a spoked aluminum hub. Question is, how much material can i remove before the pulley starts distorting and going out of round? Im not sure what exactly the process is for making these pulleys or what the material is. I would think the rough shape is probably cast and then post machined so probably somewhat stable as i remove material but i just dont know. Do i need to worry much about distortion as i machine it?
If it is cast iron then it is not going to distort any that would affect it as a pulley even if it is steel because it is round it is not going to move enough to affect it, Wow that is a big pulley for a small motor like that, I hope you have a Braking Resistor to protect the Drive
Think of it like a auto starter ring gear and shrink fit it onto the aluminum hub, this will take care of any distortion it may have
2 Attachment(s)
Re: distortion of steel when machining
yep, the reason for being so massive is my rpm needs. its a 5k rpm servo and i wanted 12,500 at the spindle. 1;2.5 ratio, 80t on servo, 32t on spindle. here it is with front plate removed, second pic flipped. and yes, braking resistor installed
https://www.cnczone.com/forums/attac...d=456332&stc=1
https://www.cnczone.com/forums/attac...d=456334&stc=1
Re: distortion of steel when machining
Quote:
Originally Posted by
QuinnSjoblom
You could also make the timing pulley in plastic, which would be even lighter and could be used with a small aluminum hub
Re: distortion of steel when machining
Quote:
Originally Posted by
mactec54
You could also make the timing pulley in plastic, which would be even lighter and could be used with a small aluminum hub
I would if i had a 5mgt hob, otherwise not sure how i would do that. Ive tried to source gt2 hobs before, seems it isnt something you can just buy.
Re: distortion of steel when machining
Quote:
Originally Posted by
QuinnSjoblom
I would if i had a 5mgt hob, otherwise not sure how i would do that. Ive tried to source gt2 hobs before, seems it isnt something you can just buy.
No you have to be licensed manufacture with / for Gates to be able to get there hobs, and hob profiles, you can machine the profile of the timing pulley with "Gearotic Motion Gear design Software" software
You may have to do it with thin blanks as deep as you cutter can go and dowel them together
Re: distortion of steel when machining
Yeah i thought about that afterwards. Especially with something like delrin, could probably get it in 2 layers, or just flip it over. Its a 15mm high belt so 18mm high pulley would be enough. Would need to look at cad again but i think a 2.5mm endmill will get into the 5mgt profile so roughly 3.5D depth in 2 layers, no problem for carbide in delrin. Ive done 3mgt this way in delrin. Drill the teeth valleys first leaving material, mill around profile with larger endmill, then just final finish with the small endmill.
I emailed gates a while back to ask if their online 3d model generator of pulleys gave an accurate profile of the tooth and they replied no, but you can request up to 2 files per month from them of accurate files of gt2 pulleys. Definitely something ill consider. Delrin would make a nice light quiet pulley.
Re: distortion of steel when machining
Quote:
Originally Posted by
QuinnSjoblom
Yeah i thought about that afterwards. Especially with something like delrin, could probably get it in 2 layers, or just flip it over. Its a 15mm high belt so 18mm high pulley would be enough. Would need to look at cad again but i think a 2.5mm endmill will get into the 5mgt profile so roughly 3.5D depth in 2 layers, no problem for carbide in delrin. Ive done 3mgt this way in delrin. Drill the teeth valleys first leaving material, mill around profile with larger endmill, then just final finish with the small endmill.
I emailed gates a while back to ask if their online 3d model generator of pulleys gave an accurate profile of the tooth and they replied no, but you can request up to 2 files per month from them of accurate files of gt2 pulleys. Definitely something ill consider. Delrin would make a nice light quiet pulley.
I have all the GT profiles but can't give them out, that is why I suggested Gearotic software as there set they have is close to perfect, as you could get, the files you can get don't get you what is needed to make the profile it works like a gear tooth where you need a different cutter profile for different number of teeth cut it is the same for the GT series as well
Re: distortion of steel when machining
Im reffering to a file for a complete pulley with a specific tooth count. The gates guy said i can request up to 2 pulley files per month that will accurately represent the profile.
Re: distortion of steel when machining
Quote:
Originally Posted by
QuinnSjoblom
Im reffering to a file for a complete pulley with a specific tooth count. The gates guy said i can request up to 2 pulley files per month that will accurately represent the profile.
Was that Tec support or customer service
Re: distortion of steel when machining
Quote:
Originally Posted by
mactec54
Was that Tec support or customer service
Not sure, but i would hope neither would make that up lol. They were pretty specific about it. Said to request a pulley with a specific number of teeth and they would send the file, up to 2 per month.
Found the email, talked with michael Bruha. It was just a gates general inquiry, not sure if hes in tech support or customer service
Re: distortion of steel when machining
Quote:
Originally Posted by
QuinnSjoblom
Not sure, but i would hope neither would make that up lol. They were pretty specific about it. Said to request a pulley with a specific number of teeth and they would send the file, up to 2 per month.
Found the email, talked with michael Bruha. It was just a gates general inquiry, not sure if hes in tech support or customer service
As an Email enquiry what you asked most likely went to a Tec support, customer service would not say or offer that, even with there files you will have to regenerate it in cad and you may find you will have to use a fudge factor to generate the form which most likely will be close enough for what you are doing Gearotic is still much easier
1 Attachment(s)
Re: distortion of steel when machining
After doing some math, there was only a slight advantage of replacing the center of the pulley with an aluminum hub. About 90% of the inertia is carried in the outer inch or so of radius, so i just hogged out pockets to reduce weight there leaving enough in the center for the taperlock bushing. Inertia is now 40% of what it was. Going with the spoked aluminum center and only keeping the rim of the gear would have only made a few percent different. This was much easier and if i decide i need it better, it will require a new gear from scratch as discussed, probably delrin and aluminum. I think this will be ok though.
It was definitely cast iron, what a mess. First time machining it. Immediately after washing it, there was already a thin layer of rust on the machined areas. Any suggestions on best way to protect it? For now it has some oil on it but it will need thoroughly cleaned before installed and a belt ran on it. Maybe just paint the machined areas?
Here's a pic, pocketed out the same on both front and back. Also took down the overall thickness. Not sure why it was so thick to begin with. Pulley is for 15mm belt and the toothed area was 23mm thick. I took it down to 18mm leaving just the center at original thickness for the bushing.
Attachment 456804
