Author Topic: Building a Drag Engraver by c. raynerd  (Read 15897 times)

Offline raynerd

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Building a Drag Engraver by c. raynerd
« on: April 01, 2012, 07:32:36 PM »
After a miserable day with my cnc machine, trying to trouble shoot an issue that I`m now fairly certain lies with a totally randomly faulty TB6560 driver (sometimes works and sometimes doesn`t!!), I decided to end with some positivity and show you my drag engraver.

When I first thought about homebrew cnc I never thought I could do fine detailed line and text work and presumed it would be only good enough for cutting mdf into rough shapes! However, I read on the net about drag engraving where the spindle doesn`t spin and you simply drag a diamond across the top layer and "scratch" the surface. I didn`t have much faith but I found a few simple ideas on the net and thought I`d have a go at making one.

The commerical ones are very expensive and start with the smallest shank of 12mm. My er16 spindle can only take 10mm max and although adapters are available, I read that if your spindle can`t handle 12mm, it is likely the bearings will not be beefy enough to withstand the sideways cutting forces of dragging the tool across the work surface. Sounded sensible to me and with my little home made brushless dc motor spindle, didn`t want to risk it.

No worries anyway, since I`m making it, I`ll just make a massive body - this is actually a massive advantage as my spindle bracket is 43mm, so making a body of 43mm means I can just drop the drag engraver straight in place of the spindle!



I turned the outer body to 43mm, reamed a 12mm bore. Used 12mm silver steel which I reamed 1/4" to fit the diamond tool (this needs turning a little deeper so less is held out the top). The 12mm silver steel slots in the centre bore...ideally to a shoulder. I didn`t do this and ended up turning a little face cap and holding it on with 3 screws (can be made out in the first photo). A spring sits on top with a little brass spring stopper and then a rear end cap screws on that with an M8 thread and bolt to apply and adjust pressure onto the spring (M8 bolt needs replacing with a nice little thumb screw asap)



I`m very chuffed with the results. Setting the pressure depth and spring took a lot of scrap test efforts but got something I`m happy with.



Here I`ve attempted to fill cut, so the diamond drag engraver sweeps across in many steps to fill the letters. All was going well until my double sided tape gave way!



Talking of which...is double sided tape definately the way to go and I just need to pay more for some decent stuff or is there a better way? Also, I know double sided tape is a method used by lots of you, but how do you go about getting your bed all nice and clean again after sticking something down to it???

Chris

Offline HS93

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Re: Building a Drag Engraver by c. raynerd
« Reply #1 on: April 01, 2012, 10:25:36 PM »

I use this in a small squeezey bottle  or atomizer , a quick spray let it soak for two min and the part comes off without bending another spray and the glue is gone, it evaporates so you can re stick in 5 min. great for all round cleaning and getting rid of chicken grease on new tools.

http://www.ebay.co.uk/itm/IPA-Isopropyl-Alcohol-99-9-Pure-5-Litre-5L-/270940964296?pt=UK_BOI_Medical_Lab_Equipment_Lab_Supplies_ET&hash=item3f155705c8

peter
I am usless at metalwork, Oh and cannot spell either . failure

Offline andyf

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Re: Building a Drag Engraver by c. raynerd
« Reply #2 on: April 02, 2012, 04:07:54 AM »
The naptha fluid for "petrol" cigarette lighters (Zippos and the like) gets rid of most sticky residues and evaporates quickly. At over 1 for 100ml or so, far more expensive than Peter's isopropyl alcohol, but a can usually lasts me 2 or 3 years.

Be very careful with all these flammable fluids. I know of a local pharmacist who was decanting surgical spirit (ethyl alcohol) from a carboy into small bottles for retail. The vapour reached the  pilot flame of his basement central heating boiler, and the resulting flashback and fire killed him. 

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline HS93

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Re: Building a Drag Engraver by c. raynerd
« Reply #3 on: April 02, 2012, 05:36:09 AM »
Hi Andy I have used Ronson lighter fluid but it leaves an oily residue that stop you re sticking, you can get IPA in small bottles http://www.tmbelectronics.com/index.php?main_page=product_info&products_id=327&zenid=8471081a452664eeced16965b3675bb4 that are the same price as lighter fuel, It's Just my preference maybee some don't leave a residue.

Peter
I am usless at metalwork, Oh and cannot spell either . failure

Offline andyf

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Re: Building a Drag Engraver by c. raynerd
« Reply #4 on: April 02, 2012, 06:15:05 AM »
My current can ("Perma" brand) doesn't seem to leave a residue, Peter. I'll steer clear of Ronson, though. No point having to find a second solvent to clean up the residue left by the first one!

But we digress...

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline AdeV

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Re: Building a Drag Engraver by c. raynerd
« Reply #5 on: April 02, 2012, 11:10:53 AM »
Hi Andy I have used Ronson lighter fluid but it leaves an oily residue that stop you re sticking, you can get IPA in small bottles http://www.tmbelectronics.com/index.php?main_page=product_info&products_id=327&zenid=8471081a452664eeced16965b3675bb4 that are the same price as lighter fuel, It's Just my preference maybee some don't leave a residue.

Peter

Yikes, that's pricey; same stuff here: http://www.shinyhardware.co.uk/prods/showprod.asp?pid=16623 12 for 5 litres. I appreciate that 5ltrs may not be for everyone, and for goodness sakes make sure you decant the stuff outdoors - or well away from any chance of hitting a naked flame.

A spray mister e.g. kitchen cleaner bottle would make an ideal delivery method I feel?

I've never tried the double-sided sticky tape method. Personally, if I had the room on the stock material, I'd use a regular clamping system with something soft between pad & material to prevent marking.

Cheers!
Ade.
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Offline raynerd

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Re: Building a Drag Engraver by c. raynerd
« Reply #6 on: April 02, 2012, 11:31:56 AM »
Hi guys, I got some propan-2-ol this morning from Jessops, nearly killed them when they told me how much it was but I should have cheaper refills in the future - I was just eger to give it a go. Just looked now and Maplin have it for sale as well, quite pricy at 15 for 1.5L but less than the 3.95 I paid for only 40ml!!!!!  :doh:  I`ll order some of the net now for refills!

AdeV - the anodised aluminium isn`t cheap either and I`ve no metal guillotine so I`ve been buying it pre-cut. Unfortunately, I`ve got no free material to clamp to so it is going to have to be double sided tape. I purchased some new tape today but in all honesty, it doesn`t look much better than the stuff I already have - is this a silly question: is there a good quality double sided tape brand?

Andyf - thanks for the concerns. I will be careful with it for sure. I know all about the dangers, we were working in a lab at Univeristy and some chap was pouring something slowly from some glass equipment, looked like a burette but I can`t imagine it was. The work bench went all the way around the room, there was a little lip on the back of the bench and then for no obvious reason, a little trench about 30cm wide by 20cm deep between the back of the bench and the wall. This chap was at the other side of the room. The bloke a few students down from me lit his burner and a wall of flames  zipped around half the room! The vapour had literally worked its way around the trench at the back of the bench and ignited. No one was hurt and it only last a split second, fire/heat alarm didn`t even sound but it was a hell of a show and potentially very dangerous!

Thanks for all the advice and info.

Anyone own or seen a commerical drag engraver? - what sort of spring tension is the cutter under? I`ve no way of measuring really but are we talking a pen spring or much harder?

Offline AdeV

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Re: Building a Drag Engraver by c. raynerd
« Reply #7 on: April 02, 2012, 11:38:51 AM »
I`ve no metal guillotine

No, I've got it, remember?  :lol: It's bolted down to my welding bench now & doing a fine job on the steel that i don't want to push through the bandsaw...

Unfortunately, I`ve got no free material to clamp to so it is going to have to be double sided tape. I purchased some new tape today but in all honesty, it doesn`t look much better than the stuff I already have - is this a silly question: is there a good quality double sided tape brand?

Anything by 3M is usually pretty good (and pricey to match).
Cheers!
Ade.
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Offline HS93

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Re: Building a Drag Engraver by c. raynerd
« Reply #8 on: April 02, 2012, 02:33:59 PM »
get the stuff used for holding down carpets it is not the foam type so no movment
yes Ade that was the one I was looking for I got the last lot from them but thought when I was looking for the link it was the place I got the elbow grease spray I also got some bottles with atomizers on for around the shop and house handy for labels and cleaning the cooker's stainless steel http://www.shinyhardware.co.uk/prods/showprod.asp?pid=25135

Peter
I am usless at metalwork, Oh and cannot spell either . failure

Offline AdeV

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Re: Building a Drag Engraver by c. raynerd
« Reply #9 on: April 02, 2012, 04:56:06 PM »
Damnit, I searched eBay for elbow grease, and now I feel dirty.
Cheers!
Ade.
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Offline HS93

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Offline Swarfing

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Re: Building a Drag Engraver by c. raynerd
« Reply #11 on: April 03, 2012, 12:57:40 PM »
Chris

Why not have a go at making a Vac bed to bolt on top of your existing, just groove opposing sides of two plastic cutting boards, Holes in one of them etc etc. Use a fridge compressor as your suction source, i'm sure you will get the idea once you had time to google a bit  :thumbup:
Once in hole stop digging.

Offline arnoldb

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Re: Building a Drag Engraver by c. raynerd
« Reply #12 on: April 03, 2012, 06:07:34 PM »
Good going Chris  :thumbup:

If you're not too picky, good old Acetone from the paint shop will clean all that sticky stuff right off.  You could borrow your wife or GF's nail varnish remover, but most of those are Acetone with some oily additives added to "moisturize" after the Acetone's done its job...  Smells the same though, so keep away from pet parrots.

A good swab with the Acetone over everything before applying the double-sided tape will also help things getting unstuck.

 :beer:, Arnold

Offline raynerd

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Re: Building a Drag Engraver by c. raynerd
« Reply #13 on: April 04, 2012, 05:47:34 PM »
Hi Chaps

Got some good double sided tape and the propan-2-ol and it is a good little setup - holds strong and releases ok at the end. A little bit of a pain to release, once a corner is up and the solvent starts getting underneath it goes OK.

Anyway, I`ve been putting my little machine under some tests and I`m chuffed to bits with the outcome. I still can`t believe that my machine is actually making these cuts.

This afternoon I really wanted to put it through its paces and so I got in contact with my pal who teaches art and one of his personal interests is line art and computerised line art - or at least I`ve certainly seen his original work being lots of lineart. I sent him an email asking if he had anything already as a computer file and got a reply: "have fun! - attached:BOB.jpg"
So, the truth is, I`m not sure who Bob is or what Bob is for that matter - how very arty, I guess you have to make your own mind up. But anyway, I was chuffed to bits with how it came out. I imported the jpg in Vcarve and copied to a vector - then off we went:



Online philf

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Re: Building a Drag Engraver by c. raynerd
« Reply #14 on: April 04, 2012, 06:29:18 PM »
 :clap:
Hi Chris,

It looks to be running very well - at last.  :thumbup:

Have you dispensed with one of the round bars on the X axis?

Are you still using the same driver and, if so, did you find out what the problem was in your setup?

If you want a linear slide to replace the other round bar you're welcome to another.

Cheers.

 :beer:

Phil.
Phil Fern
Location: Marple, Cheshire

Offline andyf

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Re: Building a Drag Engraver by c. raynerd
« Reply #15 on: April 04, 2012, 07:02:54 PM »
That's great, Chris  :clap: . You must be really pleased with the machine.

Looking at Bob's portrait, I think he's the guy who begs for spare change outside one of my local supermarkets....

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline HS93

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Re: Building a Drag Engraver by c. raynerd
« Reply #16 on: April 04, 2012, 09:39:07 PM »
Looks good , handy that you can get the art work. what tape did you end up with, and what is the tip made of that does the engraving ?

Peter
I am usless at metalwork, Oh and cannot spell either . failure

Offline raynerd

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Re: Building a Drag Engraver by c. raynerd
« Reply #17 on: April 05, 2012, 03:00:56 PM »
Peter: it is a diamond tip and cost me about 16. In the pictures in the first post, you can see the diamond tipped 1/8" steel shank inserted into the lower section of the drag engraver.  The tape is unknow from my father-in-law who uses the same type at work for an important temporary holding job. It is much much better than the stuff I had.

Andy - yes, he must be the same Bob who sits outside our Tesco asking for loose change.

Phil - the video is deceptive, I have both of the original bars still attached (there is one above the top on on the video) and the linear rail which really supports and braces the whole lot. It has done the trick 100% as it not only supports the z axis, but it also supports and braces the two sides. It does mean I lose about 4mm of z height but for a solid machine, I can totally live with that.

Regarding the TB6560 - well I have a setup that works. Firstly I need to partly apologise to the TB6560, it is easy to get onboard with the TB driver bashing cart! I`m currently set to 24v, 75% current, fast decay rate (??), 1/2 stepping and it seems to be working just fine. Half of my problem was that the motor spindle is directly attached to the leadscrew and there is about 1mm of endfloat in the motor that I was thinking was missing steps. I took this up with a thrust bearing and its much better. However, if I change any of the settings and I start missing steps. My motors are 2A and ideally I`d like to set the 3.2A driver current to 50% but I`m having to run them at 2.4A by setting the driver to 75%.

Also, with 200 step/rev and 1/2 step (current setting) = 400 steps/rev  and with a 2mm pitch leadscrew = 200 steps/rev.  That isn`t very good resolution in my opinion but if I change this to 1/8 multistepping my motors start to run really slowly, noisly and jerky. I don`t know why and I don`t seem to be able to cure it. I presume I would get a better resolution at 1/8 stepping.

There is quite a good thread on cnczone about trying to sort this TB6560 drives out. I`ll probably give it a go over the next few weeks:
 http://www.cnczone.com/forums/general_electronics_discussion/110986-how_i_fixed_my_chinese.html

 

Offline DaveH

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Re: Building a Drag Engraver by c. raynerd
« Reply #18 on: April 05, 2012, 03:15:23 PM »
what is the tip made of that does the engraving ?
Peter
Peter,
The tip is made of carbon  :lol: :lol: :lol: " I'm a wealth of knowledge ot times" :D
 :beer:
DaveH
(Ex Leicester, Thurmaston, Ashby De La Zouch.)

Offline John Stevenson

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Re: Building a Drag Engraver by c. raynerd
« Reply #19 on: April 05, 2012, 05:34:42 PM »
Chris, I'm having to run my TB board in 1/2 stepping mode.
Won't run in anything else makes all weird noises and you cannot calibrate it correctly.
It differs from job to job, 1/2 stepping seems to work OK and on the little engravers it's on it works OK.

That is setup for drag engraving and has done a few test pieces, just need to get it setup to do a small production run.


John S.
John Stevenson

Offline raynerd

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Re: Building a Drag Engraver by c. raynerd
« Reply #20 on: April 06, 2012, 04:09:00 AM »
John, cheers for replying - I`m guessing that if it is making wierd noises in anything but half step mode for you as well, it isn`t just me doing something wrong.  Strange drivers...they seem really tempremental! To be fair to it, it is working just fine in these settings, you just can`t make any changes!

Chris

Offline HS93

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Re: Building a Drag Engraver by c. raynerd
« Reply #21 on: April 06, 2012, 04:13:42 AM »
what is the tip made of that does the engraving ?
Peter
Peter,
The tip is made of carbon  :lol: :lol: :lol: " I'm a wealth of knowledge ot times" :D
 :beer:
DaveH
Havent you got a web site to wreck  :) :)

 :ddb: :nrocks: :ddb: Peter  :ddb: :nrocks: :ddb:
I am usless at metalwork, Oh and cannot spell either . failure

Offline kwackers

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Re: Building a Drag Engraver by c. raynerd
« Reply #22 on: April 06, 2012, 10:20:49 AM »
Also, with 200 step/rev and 1/2 step (current setting) = 400 steps/rev  and with a 2mm pitch leadscrew = 200 steps/rev.  That isn`t very good resolution in my opinion but if I change this to 1/8 multistepping my
1 step = 1/200th of a millimetre (about 2/10ths of a thou??) in what way isn't that very good?
I guarantee backlash, play and bending moments will easily eat that up and a lot more.

Worth pointing out that microstepping isn't a method of getting more resolution, it's mainly to make the motors run more smoothly. When microstepping the microsteps aren't linear interpolations of 'proper' steps. Half stepping is as good as it gets in terms of accuracy.

Offline raynerd

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Re: Building a Drag Engraver by c. raynerd
« Reply #23 on: April 06, 2012, 05:01:30 PM »
Kawckers- that is well pointed out and I consider myself told!!!  :whip: :whip:

Your totally correct, I`m currently going to be getting 1/200 of mm resolution! I`m still curious as to know why I can`t get the driver running with annything other than half stepping.


Offline kwackers

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Re: Building a Drag Engraver by c. raynerd
« Reply #24 on: April 06, 2012, 05:09:28 PM »
TBH it's not that long ago I realised that microstepping was next to useless as a mechanism for improving resolution...

I like the diamond drag thingy though which has given me an idea. What I'm curious about is whether I could use it to score glass for cutting, or whether it would be better to use the standard tungsten wheel set slightly behind the centre line so it'll steer.