Here we go again . . . MK4

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Here is a cutaway view of the spindle showing housing, bearings, draw bar and collet system. At the top you can see the pulleys for the drive and the belleville washers which hold the tool in place by pulling up the R8 collet

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I to am following this with interest. Have you decided on the size and number of the bellevilles? Also could you give more details on the drive arrangement for the PDB as I am making one for my mill but using an intensifier (small jack) to give a 7:1 advantage with 12 belleville washers. From a post on the Zone by SDM

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Originally Posted by Clive S

I to am following this with interest. Have you decided on the size and number of the bellevilles? Also could you give more details on the drive arrangement for the PDB as I am making one for my mill but using an intensifier (small jack) to give a 7:1 advantage with 12 belleville washers. From a post on the Zone by SDM

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Hi Clive,
I'm only 50/50 on making the spindle+PDB as it is quite a risky project, and could well end up just using the WC spindle as direct drive. But in terms of spec for the PDB system I've not finalised on all the details. It does seem quite hard to find definitive numbers on things like tool pre-load.

I'm away from my home PC at the moment, where all the data is, but from memory I'd put in the same number as the Tormach PDB kit shows (~6?) since I would be using the same R8 collet style. I've read that the load applied using the Tormach PDB kit is OK for general work but could be on the low side and an aggressive cut could pull it out of the taper, so I could need more. They don't want to share the spec details (understandable) for the bellevilles so no more data than this. I can add more than this without a problem.

I've downloaded a calculator to work out loads depending on series or parallel arrangements and also give the total travel until it bottoms out. This is where the tricky bit is to ensure the loads and travel all work out.
I had allowed for 10mm total travel of the drawbar to release the tool, of which 6mm is used to remove the pre-load off the taper, and the remaining 4mm is to push it out and hopefully release the tool.

The mechanical drive system needs a lot of force/torque, so the 7:1 jack you are thinking of is a good start. I currently have a geared down stepper driving a 1605 ballscrew. I did look at a 1204 screw to get more ratio but the axial forces are very high and I didn't want go that route in the end. Again from memory it needed at least 8 Nm to turn the ballscrew. That's all I have for now.

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I've downloaded a calculator to work out loads depending on series or parallel arrangements and also give the total travel until it bottoms out. This is where the tricky bit is to ensure the loads and travel all work out.
I had allowed for 10mm total travel of the drawbar to release the tool, of which 6mm is used to remove the pre-load off the taper, and the remaining 4mm is to push it out and hopefully release the tool.

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Thanks for the info. From what I have read (and I am no engineer) a R8 collet requires a holding force of about 2400 lbs to be safe. I am using part No. D2315162 washers from Belleville Springs 2 in P and 6 in S this give a free stack height of 28.5mm and a flat height of 24mm. 75% deflection height is 25.13 mm with a load of 12337N.

The guy on the zone recons 0.5mm will release the collet after the pre-load has gone.
The setup requires about 180Kg on the jack to give me 1260kg

I would be interested in the link for the calculator

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Originally Posted by Clive S

Thanks for the info. From what I have read (and I am no engineer) a R8 collet requires a holding force of about 2400 lbs to be safe. I am using part No. D2315162 washers from Belleville Springs 2 in P and 6 in S this give a free stack height of 28.5mm and a flat height of 24mm. 75% deflection height is 25.13 mm with a load of 12337N.

The guy on the zone recons 0.5mm will release the collet after the pre-load has gone.
The setup requires about 180Kg on the jack to give me 1260kg

I would be interested in the link for the calculator

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Hi Clive,
I got the info together last night but no time to post out. Similar to your findings.

R8 needs 2500 lbf (11,000 N or 1,100 kgf) to hold it, maybe a bit more to be safe
Used calculator on this website:
http://www.meadinfo.org/2009/07/bell...ck-design.html

Used washers (())(( to get 15,000 N when flat.

Release distance was about 0.3mm (between holding load and flat load).

Looked at data on this site:
http://www.leespring.co.uk/browse_ca...=&pageNumber=8
part 500-125-1125

This was a quick look, I think it could be refined.

Mini update -

Cut out the 3rd bracing piece:
Attachment 21222

Final one under way:
Attachment 21223

All 4 profile ops done:
Attachment 21224

Then onto the side ops. I need to machine several side features starting with 2off 6.8 pilot holes (to later take an M8 thread). Bit nervous as I'm trialling fusion 360 for the first time as it can do these pilot holes as spiral bores. Done a few aircuts and all seems OK from a cutting point of view (apart from that G28 as mentioned in another post).

Here is the fixture:
Attachment 21225

Luckily I had planned ahead (!?) and the first triangular brace I made with the poor surface finish could be used as a support. It will be sacrificial as one of the ops will cut into it.
The vertical angle is held by the precision vice, with a backstop at one end. The part just drops in and is then clamped. I was just about to hit cycle start and I was called away ! So it will have to wait . . . .

I've been busy with other projects but back on it again and ready for some updates. I've had to re-read the last few posts so see where I'd left off so apologies if I repeat something.
Last time I left you in suspense over the holes in the side of the bracing pieces. Here they are being machined:
Attachment 21557

All 4 pieces machined:
Attachment 21558

Two of the holes need to be M8 tapped, and one is a clearance + counterbore. Here is the counterbore being done.
Attachment 21559

Bit nerve racking for 2 reasons. Firstly the pilot hole was machined blind on the other side, so I had to hope I'd got it all lined up so that the counterbore appeared in line with the hole. As you can see it was all OK:
Attachment 21560

Secondly, part was a bit close to the chuck. I'd measured it and knew it would clear. Clearance is clearance as they say but still glad it went OK. . . .
Attachment 21561

Then tapping the M8 holes on the bottom:
Attachment 21563

All 4 parts done:
Attachment 21562

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Then back to the side panels. They needed holes on the sides which is always a bit more awkward. Got them dialled in:
Attachment 21564
Attachment 21565

Machined the holes and noticed that the top edge had a slight climb to it across the width with one edge 0.05 higher than the other. I guess this is reaching the limit of my current machine when cutting out a profile. So I took a very light skim to get it square again. This needs to be square to make the whole box square:
Attachment 21566

Repeated for the other one, then placed them machined edge side down onto an assumed good reference surface (lathe cross slide) to get them level with each other and then clamped them together:
Attachment 21567

Then machined the other edge, by taking a minute skim off, and then machined out the holes:
Attachment 21568

Then tapped the M8 holes:
Attachment 21569

Final dry fit of everything:
Attachment 21570

More to follow . . .

The tram plates also needed holes in the side. Here was the set up:
Attachment 21571

These holes needed to go all the way through the part, which is quite wide. The cnc machine can bore about 20mm into the hole, so the rest would need to be drilled out. But I didn't trust the drill not to wander so machined the bores on BOTH sides of the part using this fixture. Then drilled it out on the pillar drill from both sides until it met roughly in the middle. Guaranteed to get a straight hole !
Attachment 21572

Then counter-bored to hide the cap head and cleaned up:
Attachment 21573

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Onto the Z stepper mounting plate, which will hold to the 2 stepper motors. First time using Fusion360 so a bit worried about how it would turn out (didn't need to worry as it turned out and have not looked back). Exported the part as an IGES file from my CAD programme and used F360 for the CAM. Very impressed with it. Here is the part to be machined:
Attachment 21574

As you can see I was still using a profile method to cut it out (hangup of using Vectric Cut2D), but have since learnt much better methods.

Holes:
Attachment 21575

Profile:
Attachment 21576

Stepper holes drilled and tapped, and done:
Attachment 21577

More to follow . . .

Next up was a little job I'd been putting off until I'd got to grips with F360. These are going to be inserts which fit inside the extrusion to connect the bed uprights. I'm sure there are many ways to make these parts but I decided to get some practice on adaptive tool paths. Here is the first of 16 parts:
Attachment 21583

It all started with a large 8mm sheet:
Attachment 21581

I then machined 2 edges so that the parts would be the right length:
Attachment 21582

Then over to the chop saw to rough them out to width:
Attachment 21584

Attachment 21585

Next part tool a while - machining the 3rd edge on each part in turn:
Attachment 21586

Not sure if this is good practice or not but the 4th edge I did in small batches:
Attachment 21587

All to size . . .
Attachment 21588

Then 6.8 mm holes machined (ready for M8 tap):
Attachment 21589Attachment 21590

Now onto the angled sides. I made a fixture to hold the parts which had 2 datums for alignment:
Attachment 21591
Attachment 21593
Attachment 21592

The fixture was dropped into the vice each time and aligned in Y (fore/aft) by eye as this is not critical. It only needed to hold the blank in the correct X (left to right) and Z (up and down) position.

Then a 2D adaptive to rough it out. I had intended to do a cleanup but this doubled the machining time and the parts fitted fine with just the roughing:
Attachment 21594

The adaptive took about 2.5 minutes which was not too bad. I've done 8 parts, 8 to go . . .

Nice work following with interest:congratulatory:

Lovely work as usual, well done!