Adding compression to a wood auger
still in a experimental stage but perfectly doable.
objective : add compression wood auger drill
user profile : novice, patient. also, understand this as a good exercise to learn welding, grinding and how to use a Dremel
min. required machines :
– Dremel (50$)
– MIG welder with self shielded wire (~400) ; forget about stick welding this, it’s creating too much slag
– Angle grinder (~40$)
recommended machines :
– TIG welder to build up better and faster material (filler rod is cheaper than MIG wire). You can use also stretched spring (is called also ‘music wire’).
– hand belt sander, always recommended for extrusion screw making / rebuild
– bench belt sander, optimal to remove spatter
– around 50 – 100 $; possibly 20$ in electricity
– create a fixture as seen below; surprisingly the screw didn’t bend much at all; keep checking and straighten it out in case; the fixture also acts as rest for the grinding part
– it takes around 1 hour for 3 cm with the min. machines alone, 30 mins with better tools
open & todo
– can someone try this with a low-budget MIG welder, I am not quite sure there will be too much slag
– find more ways to build material, i guess brazing is out but i will try
Good topic. I take it as long as the gap decreases towards the tip, how precisely it does it is not that important. Following that thought, I was wondering if it would be easier to do the opposite and start with a large (25 mm, 1 inch) concrete bit and use an angle grinder to reduce the root diameter. https://www.harborfreight.com/16-in-sds-masonry-bit-set-5-pc-62794.html
I have not tried, so I don’t know how hard the concrete drills are. Since they use a hard tip the rest could be soft enough for an angle grinder with a coarse wheel.
Do you have a feel for how much torque is needed once you add compression. How much root material needs to remain on the screw?
good point. It’s not something you can really feel like micro drilling on a lathe but I know that weak welds or improper mounts will just break apart easily already if you have longer screws (good for consistency / beams) and a slight taper angle of 5-10 degree; Nonetheless, the wood auger is normally brutally hard; luckily the barrel keeps it in place I guess. I don’t know the grade of a SDS drill; I think it will hold up enough with this application; clients will tell 🙁
for now I’m considering this only as experiment and I’d say adding at least a taper to 20% of the auger length should improve already the result.
I guess as long as you don’t reduce the root diameter to less than the SDS interface diameter you are not reducing the strength.
Looking at your welding/grinding jig. If you were to make an insert or saddle for that opening, and for the SDS bits, if it had two fingers that protruded down and indexed against the flutes on each side of the section you are working on, then as you rotate the bit (and it moves axially) you are always positioned correctly for the part you want to grind. Then if you add a way to hold the angle grinder at the correct angle and height, you can mimic the threading function on a lathe by slowly rotating and feeding the bit in and out. The height of the angle grinder would set the diameter for any particular location.
If that didn’t make sense, I try to make a sketch.
that would be great; i tried hard; normally on the lathe this is an easy thing to do but let’s see how this could work without. thanks a lot.
Here is a cartoon of the grinding configuration I was thinking of. The SDS masonry bit passes through a block that has the grinding wheel (angle grinder, die grinder, etc.) mounted at the correct angle. The block has a pin that picks up the flute of the masonry bit. As the bit is slowly turned the block moves along the bit, keeping the grinding wheel on the root of the screw. There probably needs to be some preload on the block so it stays indexed against the pin. You could also make the block out of something softer and self tap the bit flutes into it and have the block act like an acme nut. If you didn’t want to grind, you could also clamp the block on a mill and have the masonry bit travel back and forth as you cut the root away with an end mill.
yup, that is more or less the way for larger conventional screw cutting machines; just that they push the screw through. that’s a good setup worth being tested but for now I can tell you here in the home shop if you start from a SDS drill or some basic profile, the best is to make it turn and then add the taper – freehand – with an angle grinder; not even a follow rest or anything. after adding the taper; you just keep going with the hand belt sander, 2-3 hours. Sometimes I cleanup and blend-in accidents with the Dremel. The documentation for this type of process is on the way; I am just looking for the cheapest way to get a turning device but I guess I just point to DIY alternatives on the web. Thanks Stan.
I like the idea of this. I’d be keen to give it a go.
I’m developing an auger style extruder for a 3D printer and being able to generate compression in the melt is a key factor in getting a quality result.
I looked at turning my own screw on my lathe but even the largest pitch thread that my lathe could turn was still far too fine for it to work in this application. I’m sure it would be possible on an NC machine / lathe but not on a manual one.
With the auger grinder, if you take a look at how you sharpen a fluted cutter on a tool and cutter grinder, what normally happens is that the cutter is held between centres and allowed to free rotate. The grinding wheel is in a fixed position.
There is usually a small finger that engages into the flute of the cutter. This is also fixed
As you move the cutter back and forth, the finger causes the cutter to rotate so that the cutting edge of the cutter is always presented to the grinding wheel.
hey, nice to have a real tool maker on board. yup, a setup like this could help a lot.
Regarding manual lathe, I am happy to tell you, it gave the best results after trying all other sort of things, including NC. Problem with NC is that it takes super long time to dial in a program which can cut the lower taper but also deals with shatter, increasing badly at some point; I found my self chasing my tail… Even a custom made follow rest for the job didn’t help much with the workflow since the bur tends to bend the screw even more… However, I’ve seen a more successful setup from andyn. Possibly I will try NC again but create a macro which outputs GCode for various sections but still; you wanna feel the most; things can go terrible wrong, easily.
After having done over 20 screws now manually (25mm – 35 mm diameter, 70 cm long, 22mm pitch), I am pretty satisfied with a bunch of custom grinded HSS cutters and traditional hand belt sander. In comparison, NC cutting would probably last 2-3 times longer and the result wouldn’t catch up remotely with the manual way. You want to take all into account: motor config, plastic type, screw diameter & plastic flow. Anyway, the manual process takes still 9-12 hours in total (3 hours grinding). The documentation for this is in progress. And yes, you need the largest home shop lathe you can get for this.
I’d consider this even a handcraft on it’s own, nothing you should do at home 🙂
Yes, I just watched andyn’s video, very nice.
I think manually grinding could also be an option for me as I’m making a small diameter extruder, so the amount of time to do the work is greatly reduced compared to a screw the size you are making.
Plus for me it’s likely a one off.
Are there any precision requirements on the grind? My understanding is if you are removing material from a SDS masonry bit for example, as long as you leave the flutes in place, and there is a general diameter growth in the root, if it is lumpy, does it drive anything? Does it cause bending? Or is it OK?
i am not 100% sure i understood all but I just went over to the shop :
1. holding the SDS drill against a cheap grinding wheel : eats it like butter, seems to be mild steel after all; and yes, it bends easily (that’s why manual) but I am also surprised it didn’t cause any strong shatter as I am used with the other materials. However, it grinds it so nicely, you gonna have it easy to finish it.
2. dremel whilst turning the lathe : less tool marks but way longer to do; I’d do some roughing first as 1. and do the full process with grinding paper (from 80 to 2000 );
conclusion: just do it all manually; the post processing with the grinding paper needs a turning device running at least at 800 RPM to make this quick. you get an ultra nice finish. for the perfectionists : a short look in the machinery’s handbook on grinding wheels (your bible!) may give you some better advice but looking at the sparks, it’s all ok. There is no good way to make the compression section with a wheel like that. You have to penetrate the root at least by 20-30% of the root diameter and the do the grinding paper finish. I left also some pictures about extrusion screw designs in the library.
Thanks, Yeah, maybe hand held on a bench grinder is the most expedient. I’m still not sure why it needs to be smooth/polished
if you look up on youtube ‘extrusion screw making’ or similar (check the long version); folks will tell you that it has to be a high polish because you don’t want any plastic sticking to the screw. this is quite different from traditional screw making where friction is a key player but rather for large injection molding. My first screws also didn’t got a good finish but inspecting them on the customer site didn’t unveil any good; it’s near impossible to clean it up for a rebuild.
Thanks for the photos.
I think if you had a grinding wheel the width of the spiral root it would be okay, you could then hold the bit perpendicular to the wheel. This may mean that a hand held grinding wheel (5″ angle grinder) is more appropriate as it has a narrower grinding wheel, however, that may present some issues with workholding (holding just the bit is obviously much easier than having to hold both the bit and a grinder).
You are also correct, the material is just mild steel, it is only the bits on the end that are hardened (usually tungsten carbide soldered into position).
Had a bit of a eureka moment.
Why modify a wood auger or SDS bit? Why not use the auger as a pattern to manufacture a completely new screw from scratch!
I’ve come up with a concept that is pretty easy to build and could easily be built with hand tools.
See if you can figure out my idea from the photo 😀
If not take a look at my blog for a better explaination… https://deeemm.com/index.php/entry/general/improvements-to-a-wood-auger-based-plastics-extruder
Great write up; thanks a lot for the work. I just would like to add that this post was about exploring one of the options; the more cheap an easy one can do. It’s basically only one part of a bigger series : making an extrusion screw 🙂 So for now, I can just conclude that this additive variant for the wood auger is possible but requires a lot patience and time. To stay on topic, I am creating a new topic this days: ‘extrusion screw from scratch on the lathe’; and now with your idea; we have a new candidate: ‘extrusion screw’, via ‘ DIY copy/grinder machine ? Would be great if you create a new forum topic for your build.
thanks a million
Yes, getting a bit off topic 😀
I am prepared to have a go at welding the auger as per the OP.
I have a TIG, which I would assume will produce similar results. I also have gas welding equipment (oxy / acetylene) so could try that too. I would imagine that the gas would give a smoother result that does not need much additional finishing as you can get the filler to flow a bit nicer than with the TIG (depending in filler material), however it puts a lot more heat into the workpiece so distortion may be a problem.
Brazing / Soldering would also be another option, this is generally a lot less heat than oxy-acetylene, but the type of solder would need to be chosen carefully so that it remains solid whilst in use.
Will try to make some time over the next week to do a test.
Also keen to make a screw from scratch using the idea I had, so will create a thread for that when I have something further to report.
great; the TIG variant is indeed much nicer but it’s a little off from DIY; here we need even an insurance to get Argon and it’s insane expensive that we are forced to buy it next country. What’s left is the MIG variant and I think we can leave it there; However, I am adding your notes about it to the page.
The more I think about, I really love your copy-grinder machine idea; basically like a key copy machine. Would be great if you proceed there instead 🙂 I think there is quite material in the books about copy machines. Will explore this closer this evening as well. thanks man, great job.
so now my mind is thinking…
the manual grinding idea posted above with the angle grinder and bit as a pattern.
This device could be 3D printed…
Alternately, I think we could 3D print a geared grinder using thread rod. the big issue is that lathes do not have the right gearing to turn the pitch. Yet using a angle grinder we do not need the stiffness of a machine unlike a lathe, so we could use ordinary pipe for the lathe ways. Print reduction gears sync it all together.
Maybe a thousand dollars in materials and work?
thanks @btmetz; Indeed, there is an urgent need to make screws more easy as possible for most here; I will comment only on the lathe part: i don’t know your lathes but our average 1000E lathe from the 60’s does 34 mm pitch and i could go higher doing custom gears and if that is not enough you run it via custom lead screw on a stepper. However, with the average motors used in PP; you’d need a pitch max. 22mm; that’s for 25mm screw diameter; 800W/1500RPM/1:30/3Phase and it’s doing just fine, pretty awesome 4×4 beams; I’d even recommend a pitch of 18-20 mm and 1.2 Kw because PP plastic needs a little longer in the barrel than virgin resin.
I am near finish my investigation regarding PP screws; leaving us with 2-3 ways. The optimal device can be done for 2000E with insane work, yes but once done; it may create 30 screws a month. The method used isn’t much different from industrial screw making in an Indian shop; a modded lathe.
So in the interests of efficiency and costs, at the expense of some precision. A panto-graph with a grinder would be ideal.
Maybe this sounds dumb…
can I 3D print and cast from aluminum bronze?
I can print and cast, so no worries, but will the alu bronze be durable?
Oil extraction machines with compression screws are cast, that is why they are so low cost.
@btmetz: yes, you can : https://davehakkens.nl/community/forums/topic/building-a-wax-extruder-using-lost-wax-casting/. Still doable in the homeshop but requires quite some skills compared to the simple turning device & angle grinder variant. Besides; this hasn’t been tested for plastic yet; I assume quite some wear-out and other problems. I guess it creates some backflow over time; which isn’t too bad for consistency 🙂
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