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Tool post grinder build Clough42 inspired
PekkaNF:
There is excelent YouTube series: Making a Toolpost Grinder by Clough42
Playlist of the whole series.
Drawings etc.
http://clough42.com/2018/05/24/toolpost-grinder-part-24-first-test-grind/
First I have to complment him of showing his process. Very well represented and most ideas are clear and well put. One of best I have seen.
However, it would not be me, if I would't think that while it is very inspiring and well though, there are some features that i will take different approach.
I plan to use same over all design and most dimenssions as they are. This is no problem, because he basically worked with metric parts and dimenssions and when not, he showed the rationale.
I'll be most likely using 400W BLDC motor, that lost it's ER11 chuck on the other thread.
https://madmodder.net/index.php/topic,12957.0.html
I am torn between using a very good ER20 C20 extension or the one I don't have any use, but it is little minus tolerance on C20 shaft and 0,03 mm TIR on the ER-cone.
The part I am planning to deviate from original design is bearing arrangement and mounting.
While the original design relies threaded caps to fasten the bearings onto spindle body, I am thinking to mount them a little differently.
One clear departure is that I'm not using threaded caps, other how free brearing is mounted I will make two exra bosses to aid bearing removal, if it ever comes necessary. Front boss will have bit over 20 mm holes and will have light press fit into spindle housing. When front bearing is removed , 25 mm rod can be pressed inside of the spindle housing and this will meet the ID20 mm boss that will push the front bearing out at outer race (plan is to prevent brinneling through balls).
Front bearing will be fixed (as in the original design), however I'm planning to use light press fit and glue if necessary. Front bearing has a light press fit onto spindle (ER20 C20 extension), possibility to glue. There will be spacer/flinger on the spindle to locare the spindle onto front bearing inner race.
Rear bearing will have a sliding fit onto spindle body and it will be preloaded with a wave washer outwards. prper preload of this wave washer is when it is compressed to 1 mm wide space. There is a lgiht press fit boss, fairly similar than to eject the front bearing, but here it is to size a 1 mm space for the wave spring. I though that while the belt drive will most likely guarantee mininimum loading for the rear bearing to prevent balls from skidding and wearing out the bearing in no time, does not hurt to make it proper way. While lightly loaded bearing arrangement of this kind can work with a sliding fit between inner ring and shaft, it is not good habit when loading is higher, thus I'm considering gluing the rear bearing inner ring onto shaft, when it has proved to work and preload is established.
Some pictures of the progress this far.
PekkaNF:
There might be a small break on this one. I'm trying to work out half decent method to make a grooving tool for J-section polyvee belts. I know that 55 or 60 degree threading tools are used, but I am going to try to make tools close to 40 degrees. I am thinking of grinding HSS blank or 35 degree tungsten insert.
djc:
--- Quote from: PekkaNF on August 31, 2019, 04:04:14 PM ---There might be a small break on this one. I'm trying to work out half decent method to make a grooving tool for J-section polyvee belts.
--- End quote ---
Have you seen this thread https://madmodder.net/index.php?topic=8306.0 ? You are overthinking this. Use a standard 11tpi pipe chaser die (25mm or up European gas thread) and be done with it.
PekkaNF:
--- Quote from: djc on September 01, 2019, 05:49:47 AM ---
--- Quote from: PekkaNF on August 31, 2019, 04:04:14 PM ---There might be a small break on this one. I'm trying to work out half decent method to make a grooving tool for J-section polyvee belts.
--- End quote ---
Have you seen this thread https://madmodder.net/index.php?topic=8306.0 ? You are overthinking this. Use a standard 11tpi pipe chaser die (25mm or up European gas thread) and be done with it.
--- End quote ---
Yes I have seen that. And NO, I am not overthinking this. YT build uses about 250W motor at 3400 rpm, two rib J-section belt. I'll be using 400W motor at 4000 rpm max and only slightly lower transmission ratio, around 1:1,7. Where do you get this "overthinking" part? The belt calculation programs I use indicate that it is bit marginal at 40N/rib belt tension with the length of the belt and sizes of the pulleys.
PekkaNF:
Went trough two different calculation program and few tables....it should be pretty standard, but belt is short and under 4 ribs is nonstandard. Calculations were made for Poly V-belt PJ 362 I.E. 140PJ and driver 57 mm dia, driven 34 mm dia.
More than few tables suggests that using this configuration and avoiding smallest pulleys PJ Poly-V can reliably transfer least 200w/rib at these rpms.
Talked to one design engineer at my work and he said that the calculation programs he uses allows easily over 200w/rib (four ribs) on the pulley sizes and spacing, without tensioning wheels, no problem there - in priciple. but it is not that clear cut.
But cutting down amount of ribs does not work linear because the there is less material to support the cords. Cord is spirally wound and when belts are cut from the sleeve the edge will have open cord end. Therefore going under four leads fast into compromise.
Another factor is that apparently this type of ribbed belt does not actually work like ordinary grouped V-belt. Apparently it can't really work with one rib only, needs two ribs least to stabilize and edge most ribs are not the most productive ones.
Therefore choices are:
1: 140PJ4, Standard belt, four ribs, only too wide and this will make set screw spacing somewhat difficult.
2: 140PJ3, Available, fits->this will be my choice.
Probably pure guess would have given close enough answer, but now I feel better :scratch:
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