New build – input/comments appreciated

[ngundtoft]

Can you please tell me what these profiles are called and where you can buy them. It looks like they are approx. 100mm high in the first of your pictures. I have searched the net, but I have not found the same profiles.


One more question - what distance approximately should you aim for between the tip of the spindle and the bed (steel frame), in the down position?

[JAZZCNC]

Can you please tell me what these profiles are called and where you can buy them. It looks like they are approx. 100mm high in the first of your pictures. I have searched the net, but I have not found the same profiles.

In the first picture It's an equivalent to ITEM profile size 120x80 with 8mm slot. Called Profile 40 I-Type Slot8 from Motedis in Germany.
http://www.motedis.co.uk/shop/Slot-p...60bnk0tfjmi0i0
You will need spacers with this profile for the BK/BF12 blocks as the slot hole spacing doesn't match.

The smaller narrower machines use 45x90 Profile B slot 10 and they do match the BK/BF12 blocks.

Other option is don't use BK/BF blocks and machine the bearings directly into the gantry sides and buy slightly longer screws.

One more question - what distance approximately should you aim for between the tip of the spindle and the bed (steel frame), in the down position?

Hard to answer because it depends on several factors like longest tool length and Max material size your likely to want to cut. Best way is to make a call on the max material thickness and the longest tool your likely to need and Add together plus 10-20mm extra.

For the amount of Z axis travel then I wouldn't go past 200mm with 150-160 giving a good balance of range and strength. The longer it has to extend the more it flexs so keeping short will be stronger but could limit you at some point with longer tools.
Too long and your weakening the machine. No point having 150-200mm travel when your only ever using tools that extend from spindle 50mm and cutting material less than 50mm. All your doing in this case is introducing risk of higher resonance which affects surface finish and accurecy.

This is why people who want a wider material cutting range opt for the adjustable bed because they can keep the strength and still have option of cutting thicker material with longer tools. The machine in Post#9 has this feature so can accept 150mm thick material and cut thru it with 150mm length for making mortice and tenions in 6" Oak beams or V-carve/relief the face of 310mm thick beams.

In normal day to day use the bed mostly stays in one middle of the road position.

[kingcreaky]

Well done sir.. Salute.

only thing I can suggest, is, instead of driving each shoulder of the gantry with its own stepper motor, connect the two ballscrews with a long belt to one stepper. you wont regret it. That way you can calibrate it square once, and it remains mechanically fixed that way going forward.

I think a few of the boys have done it, most recently mr njhussey look at his thread

matt

[ngundtoft]

I don't know if it is necessary, but I think the cover plate over the X-axis ballnut holder will stiffen the holder in the x direction.

Kingcreakys suggestion to use only a single Y-axis motor and use a belt instead, sounds very interesting. Obviously you save a motor and a driver and you avoid any misalignment between the two gantry sides. This is a fairly heavy machine.
Do you think that one Nema 23 motor is sufficient to do the job?


Obviously the top cantilevers at the rear of the machine, after having extended them, will obstruct a belt. Extending them gave me an extra 153mm, so that the spindle could Work 70mm in front of the frame, which is a fairly small work area for dovetails. So I was thinking if I only extended the front end rails I could fit a belt and I would have 153mm length for the dovetails, which I think would be plenty.


JAZZCNC - I noticed on your Pictures, that you are using a lot of proximity sensors. I was planning on using micro-switches, but maybe the proximity sensors are more reliable? Do you prefer magnetic, capacitive or inductance types?

[JAZZCNC]

I think a few of the boys have done it, most recently mr njhussey look at his thread

What you mean a few have done it I practicly invented it, all them other buggers just copied me. .

But he's right it does work well.! . . . . Not pretty but affective.!

I don't know if it is necessary, but I think the cover plate over the X-axis ballnut holder will stiffen the holder in the x direction.

Yes it's very necessary and I'd suggest something a little stiffer than that thin plate. Look a pic #2 and you can see the kind of stiffness i'm talking about.

Kingcreakys suggestion to use only a single Y-axis motor and use a belt instead, sounds very interesting. Obviously you save a motor and a driver and you avoid any misalignment between the two gantry sides. This is a fairly heavy machine.
Do you think that one Nema 23 motor is sufficient to do the job?

No for gantry this weight you'll really need nema 34 around 6nm with high voltage drives. The machine in Pic 2 uses twin screws joined with belts running a nema 23 on 70Vdc and while it very works well this is about the size limit of machine I'd fit it on.

Obviously the top cantilevers at the rear of the machine, after having extended them, will obstruct a belt. Extending them gave me an extra 153mm, so that the spindle could Work 70mm in front of the frame, which is a fairly small work area for dovetails. So I was thinking if I only extended the front end rails I could fit a belt and I would have 153mm length for the dovetails, which I think would be plenty.

Personally I would have a little at both ends. Think about the future or upgrades like 4th axis.? Passing the front with enough length will allow a very easy and neat 4th axis to built into the machine without impacting the cutting area.
The extra cost of longer rails or ballscrews won't be that much and usabilty of the machine is much higher. The extra functionality will return the cost 2 fold when you come to sell it or pay for it's self within a few jobs.

JAZZCNC - I noticed on your Pictures, that you are using a lot of proximity sensors. I was planning on using micro-switches, but maybe the proximity sensors are more reliable? Do you prefer magnetic, capacitive or inductance types?

Prox switches I use are inductive and they are much much better than low/mid end mechanical switches. Cheap as chips and very accurate.
I posted a video showing how repeatable they are.! . . Excuse my horrible voice!!

[njhussey]

What you mean a few have done it I practicly invented it, all them other buggers just copied me. .

But he's right it does work well.! . . . . Not pretty but affective.!

Unashamed copy in my case and proud of it.....I can vouch that it's not pretty but it will do until the machine cuts it's own replacement part

[ngundtoft]

I have stiffened up the X-axis ballscrew nut mounting by increasing material of bracket to 30mm, increasing cover plate to 10mm and inserting a 20mm triangular support.


I feel somewhat uncertain with respect to using a single motor and belt setup for the X-axis. I remember reading that the Nema 34 motor should normally be avoided because acceleration is much slower than the 23. So do the advantages (better alignment, single motor) make up for the drawbacks (lower acceleration, long complicated belt)?

Maybe a long belt could just go below the top cantilevers (and the bed) by using some extra idler pulleys?

[Neale]

..and once the machine is set up and working, you'll use it to remake components to look better? That's what I keep telling myself!

[Clive S]

I think you will need more teeth in mesh on the motor there are several examples of how to do it on the build logs.

[JAZZCNC]

I'm Going to contradict myself now..!!! . . . If your not going straight across with the belts then I wouldn't bother has it's very complicated and messy with belt that long winding around the machine. Keep it simple else stay with Slaved Motors.

Yes the belt approach is much more reliable and gives great piece of mind your always in sync. But not if the setup is overly complex it's needing constant attention and with belt this long threading around the back I fear it may cause trouble.?

So I'd say either change the design and keep it more direct or keep with slaved motors which if properly tuned and connected to good drives don't give too much trouble.