[peteeng]

Hi All - Been working thru the Z Axis. The ballscrew is a bit tricky as the BST dwgs are incomplete. But I've sent some Q's to BST. I went back and looked through this thread to see what I've done in the past. I also did a quick FE to check the deflection of the Z axis assembly. My target is 10N/um but only got to 4N/um. I thought about making the plate 8mm but then the flaring allowance for 8mm bends is bigger then the 6mm which means it would be much wider. So 6mm it is and I'll use YaG to make moulds for a composite Z plate in the future... Dwgs are coming together, found a few holes missing but so far so good... Peter

[peteeng]

Hi All & Sundry - Whats the collective noun for Tools? Since I have been working on the Z Axis I thought I'd better check what Z movement I have. The gantry is 245mm off the base so I adjusted the tool to be same. Can't put anything in higher then the air between the gantry and base. Then moved the Z axis down to the bottom of its travel and this is 220mm which I'm happy with. Target was 250mm but things change along the way. To extend it would need to be in the rail hole module of 60mm so the next step would be 290mm which is a bit tall. I'd also have to change the wall height and they are now on order so its a frozen object. Onward to check the gantry... Peter

[davida1234]

Hi Peter,

Developing nicely so far. With all your attention concentrated on the gantry and the Z-axis, did you do a load analysis on the side walls of the frame?

[peteeng]

Hi David - Yes early on included the machine base in the FE. Too late to consider now as its on order. Will measure stiffness and compare to models when built. Regards Peter see post #45 #96 early full models

[peteeng]

Hi David- Ask and you shall receive... On review I have not done any FE on the machine base in some time and I have made many on the fly decisions about it, like ordering stuff without a final FE. So right now I did a full automatic set up of the current YaG in Simsolid. Looks Ok without digging too much. The walls deflect 0.01mm while the tool deflects 0.37mm at a 1000N (101kgf) tool load which is 2.5N/um static stiffness. I used 3500MPa for the MDF stiffness. I think its about 4000MPa when skinned in melamine. So happy with that. This model also has the shear brackets on one side so I'll look at those... There's not much delta between brackets and sans brackets so looks like brackets are out . I seem to remember doing some work on this before with the same conclusion. So more detailing dwgs. Re BST motion stuff. I think this is their factory... anyone needing dwgs and specs for their stuff its found here.

Chinese Ballscrew,Linear Guide,Linear Robot,Linear Module Stage etc.- FBT INDUSTRIES

Regards Peter

I keep asking Fred for dims for things which he does respond to. The BST site recently has stopped putting snippets of dims on their site so I did a search for one of their part numbered bearings and up popped this company. Colours PN's and images are same is BST motion stuff. So good chance this is the manufacturer and BST motion is one factory outlet for FBT

[peteeng]

Hi All - Now I have a global model running I looked at the max stress point which is one of the webs on the saddle. So I'll leave out the big hole in the web. The stress is small at 37MPa but it will be stiffer without the hole. Keep Making Peter

[peteeng]

Hi All- Has anyone used the BF support bearings from BST (or other BF type from other suppliers?)? Does the bearing slide in the housing? Two dwgs here different? Regards Peter

[machinedude]

looks like the ones i have. i was not impressed with the design of the end bearing blocks simply because the only thing holding the bearing in place was a press fit and one of mine moved on me. i would have rather seen the bearing locked in a bore with a shoulder.

[peteeng]

Hi MD - so the circlip is recommended? By moved do you mean the housing or the bearing? It is supposed to be the floating end? Also means the screw can't be preloaded...Regards Peter

[machinedude]

i'm pretty sure it was the bearing moving around on me. mine had the c-clip on the end which i was not a fan of that aspect either. like you said the preloading can't be done. i got some backlash and i'm pretty sure that was at least part of the cause of that. it's on my to do list when i get time to get back to working on things but life has had other plans so not much is getting done in the machine building department

[peteeng]

Ah yes , life the universe and everything tends to screw with us. The big think computer took 4.2 million years to sort it? I think loctite is the answer to everyhing... Peter

[machinedude]

i was trying to get some light preload with that design but the press fit was pretty light on the one end block i noticed things on so that did not help. a little bit a preload on the screw helps a little bit whit screw whip so that was the reason i was trying. found out pretty quick it does not work so great

just been busy with the adults kids of mine a lot lately things are only going to get worse since i have a grandchild coming this week my oldest past her due date so the hospital has her penciled in for tomorrow to help things along my other daughter moved out but end up back pretty quick but she lost her room to the baby coming so i have been running around in circles trying to get everyone situated i feel like i need about 10 more of myself to get anywhere anymore

[peteeng]

Multiplicity the movie ended badly, don't get more then 5 of you. peter

[machinedude]

that's funny you thought of that movie i was thinking about that movie the other day but i can't remember most of it just because i seen it a long time ago. i might have to see if i can find it so i can watch it again

seems like i need to do the research first before i start cloning myself

[davida1234]

Peter,

The images you showed above about the machine base analysis looks like, as far as I understand it, only in one direction, parallel with the wall. I think it would be worthwhile to check the other direction as well. Perpendicular to the wall length.

[peteeng]

David - Good point so here it is. 0.19mm stiffer then the "push" or "pull" case. Generally speaking transverse is stiffer as the gantry is not in torsion. Torsion is the big issue with gantries. Peter

[jackjr-123]

Hi MD - so the circlip is recommended? By moved do you mean the housing or the bearing? It is supposed to be the floating end? Also means the screw can't be preloaded...Regards Peter

This is the floating end yes. The bearing is designed to slide in the housing (clearance fit). The circlip is useful to keep the bearing against the ballscrew shoulder and not falling out (for example when installed vertically).
Not sure why you're talking about preload since this is the floating end.

[peteeng]

Hi Jack - I haven't used ballscrews before so its new territory for me. I have used leadscrews with support bearings but have bought these local so I design around what I have in hand. There's discussion about how preload helps ballscrews but as you say its floating so can't be preloaded. BST got back to me about where the bearing is and its considered to be in the middle. So I can finalise the screw dwgs now. Peter

[jackjr-123]

The preload happens in the fixed support unit with 2 back-to-back AC bearings. A fixed support unit at both ends can be used to dramatically increase the overall ballscrew stiffness, but in your case I think the supporting structure is way too light to consider it.

Also, you might want to check out SYK for quality and inexpensive support units.

[peteeng]

Hi Jack - Thanks for chipping in....I've used SYK supports before on medical equipment and YaG uses their motor mounts. As you say good quality at a good price. Peter