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Thread: GT2 belts and pulleys

  1. #1
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    Default GT2 belts and pulleys

    I've been scouring the net for information about the best toothed belt drive for accuracy and minimum backlash. It would seem that the GT2 profile is favoured by many for this. But there are some very funny quirks in the system when it comes to actually getting the bits.

    Our favourite engineering store (otherwise known as eBay) features toothed belts and pulleys of course. A few vendors for most every variety and size, but in general they are all expensive and charge lots of shipping. The shipping costs from USA to Australia (where I live) can easily be double or triple the cost of the goods themselves - all many USA vendors seem to know know about is Priority FedEx. Sigh.

    However, China and Hong Kong to the rescue ... but not for everything. They are big on GT2 belts and pulleys in the 2 mm pitch - at least in some sizes. Digging into what's on offer, I find that if the parts are required for some Reprap designs they are widely available, at very good prices - but other parts or sizes are not. OK, some design cunning required at my end. There's a bit of a range of 2M GT2 6 mm wide and 10 mm wide belts available, so that's OK. But what about pulleys?

    Well, a few pulley sizes are available, such as 20 tooth, 36T and 40 T, with 5, 6, 6.35, & 8 mm bores, but nothing larger. As I need a custom design for a larger pulley (100 - 120T), I will have to make it myself. Interestingly, I was able to find two versions of the GT2 profile on the web. There are very complex drawings in the original Gates Patent 4,515,577 , but there was also a simplified version which is most usable.
    GT2 belts and pulleys-gt2profile1-jpg
    You have to start with the theoretical PCD rather than anything measurable - that's the PLD in the diagram. Roughly speaking, that's the level where the glass or steel tension members run. That's how it works. The big problem is that the cutter needed is very very thin: 1.11 mm diameter. I don't think you can machine around a blank to any great depth with that one! (Such cutters have a DoC of about 3 mm anyhow.)

    It is tempting to try to cut the teeth in bulk by drilling a circle of 1.1 mm holes, then turning the rest, but that will leave very sharp edges at the tops of the teeth, and these edges will chew the hell out of the belt. So the teeth will have to be at least trimmed one by one on a rotary axis. And of course you would like flanges on the sides.

    One way of doing this is to cut the teeth out on a rotary axis (in the usual manner) and then stick flanges on later. That's simple, except for the multiple passes needed to get that R=0.555 mm base to the tooth - which is actually critical to the zero-backlash part. So, off to eBay looking for ball-end cutters with a diameter of 1.1 mm. Unfortunately they don't seem to exist at any reasonable price.

    Aha - but ... most carbide milling cutters are diamond-ground these days on a programmable CNC machine (often German), using a canned routine driven by parameters entered by the operator. And 1 mm ball-end mills often start with a 4 mm blank: plenty of room. Could someone make me some with a 1.1 mm diameter by tweaking the parameters? After all, if GT2 uses a 1.1 mm cutter, then there could be others interested in this size as well. So I asked a reasonable Chinese vendor I have dealt with before. The answer (within 6 hours) was YES. The price was just a little bit more than for the 1 mm ones: US$25 for 5 cutters. Coating is available on request.

    Current status: we have agreed on price and quantity. Delivery will take a couple of weeks. I am getting 5 of them - I am sure to break one or two! When they turn up I will test them. If it takes 15 passes at 0.05 mm per pass per tooth - who cares? The machine will be doing the work, not me. I can cut at a reasonable speed with that DoC anyhow. All being well, I will report back with the vendor's eBay name.

    Oh yes: OD and PLD info is readily available from a PDF on the SDP/SI web site. Most helpful.

    Cheers
    Roger

    Similar Threads:
    Last edited by RCaffin; 01-10-2015 at 04:36 PM. Reason: added info


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    Default Re: GT2 belts and pulleys

    Hi did you reach somewhere?



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    Default Re: GT2 belts and pulleys

    Yes.
    Bought belts, made cutters, machined pulleys, put pulleys into use.
    What are you looking for?

    Cheers
    Roger



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    Default

    Quote Originally Posted by RCaffin View Post
    Yes.
    Bought belts, made cutters, machined pulleys, put pulleys into use.
    What are you looking for?

    Cheers
    Roger
    I would like to give it a try and do the same creating the pulley myself. Would please help me by send supplier contact. And I would appreciate if you post some photos for the pulleys.



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    Default Re: GT2 belts and pulleys

    Quote Originally Posted by Bhalddin View Post
    I would like to give it a try and do the same creating the pulley myself. Would please help me by send supplier contact. And I would appreciate if you post some photos for the pulleys.

    You can get all you need to make your own Timing Pulleys from Gearotic, they now have the GT series Timing Pulleys, you can down load the software and try it, then when you want the G-code you would have to buy the software to activate that part

    "Gearotic Motion Gear design Software"

    Mactec54


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    Default Re: GT2 belts and pulleys

    I think I bought my GT2 belts from SDP-SI in the USA. They also have pulleys.

    You can get a few sizes much cheaper off the web (from China), but be warned they are not really the GT2 profile. They may work fine with the pulleys the same vendors sell. They seem to be made for the RepRap market, which is low-power and low-speed in comparison to what a GT2 belt can handle. A market where 'most anything will do' perhaps.

    GT2 belts and pulleys-7331-jpg

    Finished pulleys, 3:1 reduction, on the Z Axis. Custom taper-lock fittings holding them on. 'Custom' => my design, my manufacture.

    Cheers



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    Default Re: GT2 belts and pulleys

    Hi Ningbo
    Yes, but there are some conditions.
    I have looked at some Chinese belts on eBay, and while they are similar to the GT2 profile they are NOT the same.
    I have found lots of Chinese belts which are 6 mm wide, but ONLY 6 mm. I want 9 mm wide ones.

    So - what can you offer?
    Cheers
    Roger



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    Default Re: GT2 belts and pulleys

    What was the vendor's name and link?



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    Default Re: GT2 belts and pulleys

    What was the vendor's name and link?
    It's not clear who you are asking.
    Cheers
    Roger



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    Default Re: GT2 belts and pulleys

    Quote Originally Posted by RCaffin View Post
    What was the vendor's name and link?
    It's not clear who you are asking.
    Cheers
    Roger
    This would be who
    Quote Originally Posted by RCaffin View Post
    All being well, I will report back with the vendor's eBay name.




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    Default Re: GT2 belts and pulleys

    Ah - that far back. It was CarbideChiu on eBay. I have bought several lots of cutters from him, and the service has been good.
    In this case the quality was a bit higher than I had asked for: I gather that was the stuff the factory was processing at the time. They were also coated, which was not in the initial request. He apologised for the slight increase in price and left it up to me to decide whether to accept the change. I did so as the increase was not much and there is no such thing as cutters which are too good. They work well.

    Cheers
    Roger



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    Default Re: GT2 belts and pulleys

    Do not use GT2. GT3 or the white belt listed in my collection

    CNC Stoof collection on eBay!

    Luthier/Woodworker/Machinist in NS, Canada.


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    Default Re: GT2 belts and pulleys

    Well ... opinions differ.
    Gates themselves (they invented the GT2 and GT3) sell GT2 pulleys to go with their GT3 belts. Obviously there cannot be a lot of difference between them.

    But the story is more 'complex'. The GT2 is known to be superior to the older HTD (white belt) by a small amount. It took a lot of work to get there. The GT3 is simply an updated GT2 - updated because the GT2 patent expired.

    On the other hand, the 'Chinese' GT2 belts sold on eBay bear only a minor resemblance to the Gates GT2 profile. The Chinese ones are a simplified copy, nothing else. They do NOT pay royalties to Gates Are they adequate for DIY 3D printers? Probably: the resolution on those printers is poor.

    Cheers
    Roger



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    Default Re: GT2 belts and pulleys

    I used GT3 belts on my first cnc. Its not a good system. They are tolerable under a dual belt set up, which is pricey and you can basically just go to lead screw for that money. GT2 is smaller then the gt3 so I can only assume they perform worse.

    Luthier/Woodworker/Machinist in NS, Canada.


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    Default Re: GT2 belts and pulleys

    Well, I would not use a direct belt drive on a CNC anyhow. A toothed belt reduction beteeen motor and leadscrew - yes.

    GT2 is smaller then the gt3
    I think you may be confusing the number in the GT2/3 name with the pitch of the belt. GT2 and GT3 both come with the same pitches and belt widths. They are interchangeable.

    Cheers
    Roger



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    Default Re: GT2 belts and pulleys

    Quote Originally Posted by jahnj0584 View Post
    I used GT3 belts on my first cnc. Its not a good system. They are tolerable under a dual belt set up, which is pricey and you can basically just go to lead screw for that money. GT2 is smaller then the gt3 so I can only assume they perform worse.
    GT2 and GT3 profile are the same, the change was for patent protection, the GT2 patent ran out so the GT3 was the new patent same product, if you have had bad performance with them you need to look at how you where using them, they are the best there is for use in motion control, they will only be of use if correctly engineered for what they are being used for, it was obvious, the way you where using them, was a fail before you started

    The belt you have a link to is not from the GT family, HTD belt pulley combination have some backlash between the pulley and belt teeth the GT series have almost zero clearance and with correctly made pulleys you can have zero clearance

    Mactec54


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    Default Re: GT2 belts and pulleys

    The copy's are crap on a 3D printer at 70 mm/sec that's there limit past that they are horrid 64 mm/sec is ok

    <img src="https://ivxo1q-dm2305.files.1drv.com/y4mENMmTr_Cabc7pR0FUdB6gtbADq2JbuG4_rGy0eBQvLJx19pTi6TqMUIJN0xgOyDIc0gWoxYhS38HpbSTFGdfaK-o42IOU6jczrhDpfpCOTNGL1X6hvZCbgj0y35gqmq1YGTrWwShYGV-C7lXA2esy0Pi_WfnBSyroDLSGXwce4uSr1U7op7srdi78rispHCa_K4aFlTlJPVkkNWMfgh_Tg?width=60&height=60&cropmode=none" width="60" height="60" />

    Being Disabled is OK CNC is For fuN


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    Default Re: GT2 belts and pulleys

    The GT2 profile was designed for about 180 degrees of wrap and a fair tension on them to seat the teeth. I dare say many 3D printers don't come anywhere near the recommended operating conditions. So ?

    See the photo in posting #6 in this series. That's a GT2 belt, and I can hold a 2 micron position on that axis, and resolve the basic 0.8 micron resolution of the drive (with a touch probe).

    Cheers
    Roger



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    Default Re: GT2 belts and pulleys

    Quote Originally Posted by daniellyall View Post
    The copy's are crap on a 3D printer at 70 mm/sec that's there limit past that they are horrid 64 mm/sec is ok
    Yes the Chinese GT pulley copy's are not the same profile as the true Gates GT profile, they are close but a poor copy, they just use the same name

    Mactec54


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    Default Re: GT2 belts and pulleys

    In my use I did have 180* of engagement. The belts are only 6mm wide, and suffer from stretch which is where their weakness lies. Once stretched, its a decent budget option but is not very efficient with the power from the motor.

    I am talking about GT3 here. My friend tried the GT2 and instantly wanted me to send him my extra GT3.

    Luthier/Woodworker/Machinist in NS, Canada.


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