Thread: Dust shoe advice needed

Hi Russell

Do a search in this forum for "Dust shoe". You should get heaps of hits.

Originally Posted by Bob Willson

Hi Russell

Do a search in this forum for "Dust shoe". You should get heaps of hits.

I did before I posted - also did vacuum shoe, vacuum foot and dust foot. GOt a few general question but not much more. I have found a couple threads over on the CNC forum that have some good info, so I'll browse around there for a while.

Russell.

yer i dont like the big shoe
if you find one please share
at the moment ive got the vacuum cleaner in one hand , lol , well you should watch it while it cuts and at least thats some thing to do

I use Kent's dust shoe on my 4x4 - works extremely well but may be a bit large KentCNC. I also did a search on youtube on Kents dust shoe and there are a couple of other designs that may be useful.
Cheers

Originally Posted by ailmik

I use Kent's dust shoe on my 4x4 - works extremely well but may be a bit large KentCNC. I also did a search on youtube on Kents dust shoe and there are a couple of other designs that may be useful.
Cheers

That's the sort of thing I want, but am going to try a DIY version as it's a bit expensive. I bought a couple lengths of pool hose yesterday, and have clamped it to the spindle. Now I just need to make the shoe to fit the connection and hold it to the spindle. Only thing I'm worried about is, whether reducing the inlet size that much will kill the suction power.

Russell.

Sorry but it does.

High volume low vacuum systems (dust extractors) are the only way to go. For that you need a 4 inch hose.

If you want to know how effecitve a vacuum works hold your hand 25mm away from a shop or household vacuum (LVHV) and you wont feel a thing. The HVLV systems pull at lot more air at that distance.

Originally Posted by rodm

Sorry but it does.

High volume low vacuum systems (dust extractors) are the only way to go. For that you need a 4 inch hose.

If you want to know how effecitve a vacuum works hold your hand 25mm away from a shop or household vacuum (LVHV) and you wont feel a thing. The HVLV systems pull at lot more air at that distance.

Hmmm. My hose has a 6" diameter I think. How the heck do you keep that mounted onto the spindle?

Originally Posted by rodm

Sorry but it does.

High volume low vacuum systems (dust extractors) are the only way to go. For that you need a 4 inch hose.

A 4" hose drawing it's maximum air flow will certainly be better than a 2" hose but the minimum flow rate and air speed needed to grab the very fine (invisible) dust at source from a high speed spinning blade is 1000 cfm and 4000 fpm. A 4" hose even on a 3HP dust extractor can easily reach 4000 fpm (as will a vacuum cleaner) but the 4" hose can only transmit about 600 cfm and a and a 2" hose can only do 200 cfm.

The minimum diam hose that can deliver the 1000/4000 spec is 6" and to do that a 2HP unit is a minimum but the pathway must remain at 6" or greater all the way to and through the impeller.

Have you tried the test I described?

There is little point making something that wont work and if you think about it why do the commercial models have a 4 inch inlet? They produce the same amount of dust your machine will.

You have been offered a solution by ailmik - alternative is to make your own with a reducer to 4 inch hose based on that design and buy his brush.

...and that's how the heck you do it

Bob,
It is just too impractical to mount a 6 inch hose on a foot of a CNC spindle unless it is a big machine. There are clearance issues and difficulties making a 6 inch hose follow at rapids including erratic sideways and backward moves of 5m/min - this machine has a cutting envelope of 600 by 400mm.

Originally Posted by BobL

A 4" hose drawing it's maximum air flow will certainly be better than a 2" hose but the minimum flow rate and air speed needed to grab the very fine (invisible) dust at source from a high speed spinning blade is 1000 cfm and 4000 fpm.

That's why you use a brush to contain the dust and chips. The brush prevents the dust from being thrown away from the tool. If you have a brush that reaches the table, and completely surrounds the tool, you don't need nearly as much suction to get all the dust.

I do agree with you about the 4" hose, though. I believe that a 2HP dust collector rated at ±1000cfm should be considered minimum for very good dust collection, but with a good dust shoe, a 1HP 400-600 cfm collector will still keep the air very, very clean. The larger ones will just pick up more of the heavier chips.
(Note that these are manufacturer's cfm ratings, which are usually greatly exaggerated)

Originally Posted by rodm

Bob,
It is just too impractical to mount a 6 inch hose on a foot of a CNC spindle unless it is a big machine. There are clearance issues and difficulties making a 6 inch hose follow at rapids including erratic sideways and backward moves of 5m/min - this machine has a cutting envelope of 600 by 400mm.

Sure I understand the limitations of a rapidly moving cutting tool I was just stating the dust specs needed to grab the majority of very fine dust

I don't know if I would bet on a brush containing all the very fine dust. Just because a machine looks like it's picking up visible dust doesn't mean it's picking up the invisible. Fine dust acts more like a gas than a chip. It would be interesting to see particle count readings in the vicinity of an operating CNC. One solution might be to put the whole CNC in a dust hood with a 6 or 8" duct.

I would enclose the whole thing and have a 100mm line from the dust shoe. From the enclosure I would have two 150mm lines clearing the air surrounding the machine. Don't forget that to draw air you must have an inlet of equal size to supply the air if an enclosure is needed/used.

Well, I've pulled off my pool hose pieces and I'll see if I can design something to hold my (checked) 4" hose inlet to the spindle, and see how I go from there.

Russell.