ejparrott Posted February 3, 2012 Share Posted February 3, 2012 Are they any experts on belt design out there? I'm replacing the drive on my bridgeport-clone, doing away with the variable speed drive and replacing it with toothed belt drive and variable speed motor. My reasoning is that the modern VSD belts are only lasting 6-9months now, instead of years and years and years, and the drive motor killed its bearings and tore up the armature, so its knackered, and at £750+VAT for a rebuild, work said scrap it, i bought it and said VFD+CNC! So, I used a Gates catalogue and designed it according to their formula for an 8mm pitch drive, which I'm now finding a bit hard to get. There's formula in the ondrives catalogue that I'm struggling with, and I wondered if anyone out there could help? I was thinking that 5mm pitch stuff, which is more readily avaliable, would be ok, the Gates formula's working out a power factor of 3.74Kw. Oh, and my reason for this not being OT, is that its technical - its about machines, and bits are made for my land rover on it....is that ok? Quote Link to comment Share on other sites More sharing options...
SORNagain Posted February 3, 2012 Share Posted February 3, 2012 I have a lathe with a variable speed drive and have been considering the same sort of conversion because of excessive wear in the VSD mechanisim. However, I was just thinking of using a normal V belt (or two). Is there any reason you need some sort of synchronous drive that requires a toothed belt? A V belt can often provide a handy clutch should something foul the cutting tool. I have always found a slipping belt is better than a snapped one.... Edit...and yes I do think thats OK! Quote Link to comment Share on other sites More sharing options...
Phil Hancock Posted February 3, 2012 Share Posted February 3, 2012 The Beaver mill(bridgport clone) uses a single V belt from the motor to spindle and i have given that some stick with a tipped end mill and not had it slip. It is an A section belt which when it finally snapped(it was very old) was replaced with T link belt. Quote Link to comment Share on other sites More sharing options...
fatbloke Posted February 4, 2012 Share Posted February 4, 2012 Havea chat with the lads at Bearingboys. i Have sourced lots of weird and wonderful toothed belts from them and they have never let me down. If you can try and get a kevlar reinforced one, that would withstand more abuse than you could hope to throw at it. http://www.bearingbo...CFRR8fAodZ0chwg Quote Link to comment Share on other sites More sharing options...
simonr Posted February 4, 2012 Share Posted February 4, 2012 I have just a tiny bit of experience or this! Bridgeport Interacts use a polyvee belt with a 9.5hp (in my case) spindle motor. The belt is about 40mm wide with about 15 V's. When you push the big red button on the front, it uses everything it's got to stop the quill quickly, usually taking out the mains trip - and the quill will go from 6000 rpm to zero in an instant! I would conclude from that that it has ample power & torque handling capability and also isn't as destructive if it does slip a bit. I've added a servo driver to the VFD and an optical encoder to the quill - which allows me to do things like rigid tapping. I fully expected the belt to slip but it just doesn't! A polyvee might be an option - they are certainly a lot cheaper than timing belts. Other options for good value belts are (obviously) car timing belts and Harley Davidson drive belts which are about 2" wide - and make pretty good caterpillar tracks! I think if I vere converting I'd use a 200Tdi timing belt then injection pump pulleys and standard idler & tensioner - all cheap as chips and not a bad length. Si Quote Link to comment Share on other sites More sharing options...
ejparrott Posted February 5, 2012 Author Share Posted February 5, 2012 An interesting thought. The reason I'd gone for toothed belt instead of V betl Phil was because of the motor mounting on a bridgeport, or Lillian in this case, there is no provision for tensioning a belt, which i usually struggle with anyway! I was going to use a tooth belt because it requies a minimum amount of slack to be able to change it, and I was going to use a spring loaded tensioner on the side, rated at figures present by the Gates catalogue. The more I look into it though, the more it looks like I'm going to have to fabricate a new top housing to support the motor in any case, and so V belt may become an option again. Its a difficult one. My motor is 2.2Kw, with a service fact of 1.7, and a fastest spindle figure of 4250, hence the 8mm pitch belt. I nesarly bought a Harley, until I found out they'd departed from shaft drive and gone to belt drive... Quote Link to comment Share on other sites More sharing options...
pete3000 Posted February 6, 2012 Share Posted February 6, 2012 hpc gears has a large selection along with data and a selector tool. htd8 any good to you http://www.hpcgears.com/ Pete Quote Link to comment Share on other sites More sharing options...
integerspin Posted February 7, 2012 Share Posted February 7, 2012 I nesarly bought a Harley, until I found out they'd departed from shaft drive and gone to belt drive... I liked the shaft drive harley. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted February 8, 2012 Author Share Posted February 8, 2012 I went shaft drive Honda instead! Some good stuff on the bearing boys website so thanks for that link...I've been looking and looking and looking and it really does look like I'm going to have to build a new top frame and motor mount anyway, regardless of whether I use tooth belt or V belt. That means we're going to be coming down to cost, and whether I'm happy getting tension on a V belt. What worries me is a V belt slipping, as I intend for this to be CNC'd, and potentially left running 'lights out' for periods of time. All the machines at work bar the other Lillian and the XYZ replacement for the Lilly I had use tooth belt drives for everything, oh and the Colchester lathe. And I know I havent got to put a lot of tension on a tooth belt. There's also the posibility of doing direct tapping at some point in the future, which would really depend on the belt not slipping. I'll have to do some more work on costing belt drives out I think, and design a fabrication for mounting the motor up. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted February 9, 2012 Author Share Posted February 9, 2012 Couple of hours studying and I think, curtesy of Bearing Boys, I have a solution. A pair of 30tooth/72tooth to give me 1:2.4 and 2.4:1 is about the best I can get - I was hoping for 1:2.86 - and a 670 belt for 206mm crs. Trouble is I could really do with a pair of 50tooth for the 1:1 mid range that I need, which isn't listed. The 48tooth on a 206crs would need the 635 belt, and the last thing i want to be doing is swapping belts as well as ranges. So, its a call to the tech department, or failing that I'll have to go to HPC or Ondrives for a mega expensive one Quote Link to comment Share on other sites More sharing options...
ejparrott Posted February 9, 2012 Author Share Posted February 9, 2012 hmmm, they can't....and ondrives don't list one either.... Quote Link to comment Share on other sites More sharing options...
simonr Posted March 9, 2012 Share Posted March 9, 2012 There's also the posibility of doing direct tapping at some point in the future, which would really depend on the belt not slipping. Err....If you are rigid tapping and the spindle encoder is on the spindle, rather than the motor it doesn't matter if the belt slips a bit. I used my mill to re-tap one of the screws on my spectacles. It was originallly M1.0 and I changed it to M1.5 as the thread had stripped. It looked crazy having a 3 Ton machine tapping such a tiny thread. Si Quote Link to comment Share on other sites More sharing options...
02jcole Posted March 9, 2012 Share Posted March 9, 2012 ContiTech might be worth a try: http://www.contitech.de/pages/produkte/antriebsriemen/antrieb-industrie/antrieb-industrie_en.html They have also got a free design software which might be useful if you can obtain a licence key. Quote Link to comment Share on other sites More sharing options...
bishbosh Posted March 9, 2012 Share Posted March 9, 2012 Err....If you are rigid tapping and the spindle encoder is on the spindle, rather than the motor it doesn't matter if the belt slips a bit. I used my mill to re-tap one of the screws on my spectacles. It was originallly M1.0 and I changed it to M1.5 as the thread had stripped. It looked crazy having a 3 Ton machine tapping such a tiny thread. Si Absolutely first class Si! As an aside, what is rigid tapping compared to normal tapping? Quote Link to comment Share on other sites More sharing options...
simonr Posted March 9, 2012 Share Posted March 9, 2012 what is rigid tapping compared to normal tapping? Non rigid tapping is where the tap is held in a slide so it can move in and out (Z-Axis) freely. The mill / drill just turns the tap back and forth. The trouble with this is how much force you need to put on it to start the thread, it varies depending on the size of tap and the material. Did the tap start cutting on the first revolution - in which case the depth of the thread varies. Rigid tapping is where the machine holds the tap rigidly and moves the Z axis in and out as it turns the spindle clockwise & CCW. It guarantees that the start of the thread and the depth will be spot on but it requires tight coordination of rotation and Z axis. Rigid tapping you can start with a No 3 Bottoming tap and you tend to get a better thread form, particularly in difficult conditions. The third method is 'thread milling'. It uses a tool that looks a bit like a toothbrush in profile with effectively a single flute of a tap sticking out from a spindle. With these you move the X & Y Axes in a circle and move Z one thread pitch per orbit in X & Y. You can use them to mill internal and external threads and you don't need any spindle indexing / control - it just spins. This is great for big diameter threads and produces a really nice result. The tooling is really expensive - but you can make a good alternative out of a straight fluted tap mounted in a boring head. Si Quote Link to comment Share on other sites More sharing options...
ejparrott Posted March 9, 2012 Author Share Posted March 9, 2012 Err....If you are rigid tapping and the spindle encoder is on the spindle, rather than the motor it doesn't matter if the belt slips a bit. Hmm.... never thought of that..even though i intended to put the encoder on the spindle..in case the belt slipped..... brain no work sometimes! Quote Link to comment Share on other sites More sharing options...
ejparrott Posted May 18, 2012 Author Share Posted May 18, 2012 The third method is 'thread milling'. This is great for big diameter threads and produces a really nice result. We've got a shaft extension in the shop with 12 M36 holes to be thread milled in the end. We usually thread mill to with .5mm of size and then run a tap though to size it, depends on ho well the material cuts but can often end up with a chattery thread when milled. Quote Link to comment Share on other sites More sharing options...
vulcan bomber Posted May 18, 2012 Share Posted May 18, 2012 On the other end of the scale, its impressive watching a m1.6 hole being milled. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted July 9, 2012 Author Share Posted July 9, 2012 5M section belts won't do what I want to achieve. The boss sizes are just too small (at sensible priced pulley level) to cater for the mill spindle that they've got to fit on. I've now identified a set of SPA section belts and pulleys that will achieve what I need, I just need to measure motor and mill spindle so I can get the right taperlock bushes to match. Quote Link to comment Share on other sites More sharing options...
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