# HDPE lathe turning, debubblizing using vacuum, stabilizing wood with vacuum/resin



## Susi (Mar 3, 2013)

This tutorial and idea collection was sparked by a question on the forum about lathe turning HDPE and I think the poster inferred made from home melted billets. He was also questioning vacuum debubblizing the melt. I've assembled some thoughts, some practice, some ideas and uses of vacuum chambers and HDPE. If you want me to edit any errors, please comment or PM me and I'll make the appropriate changes so as to render an accurate and useful tutorial.

First,know that HDPE does not react to tooling like wood, it's a whole nutha medium. It's about as easy to work as wood with hand tools but lathe work, it's gonna be different to some degree.

On vacuum chambers:
I used a vacuum chamber to debubble thick viscous silicone mold RTV compound in the jewelry mfg biz..mandatory it was, else the mold cavity would have 'zits;' where bubbles were on the item's surface to be molded, and for debubblizing gypsum/silica mold compound (like plaster of Paris sort of) for lost wax casting...a must, else countless 'zits' appear on the castings, lengthening clean up time. The viscous silicone debubblized well .I unfortunately sold my vacuum machine with the rest of my stuff when I left USA. I longed for it when one of my HDPE projects, the camo one, turned out pretty bubbly. I think a vacuum machine/chamber would work excellently with an HDPE melt provided it was done fast so the melt doesn't thicken and harden more than it is already. For bubbles to expand under vacuum and therefore rise theoretically to the surface, the medium must be liquid enough to permit bubble rise, else the bubbles just form and don't rise, rather contract when the vacuum is released, having zero effect. It's worth a try if you know a manufacturing jeweler with a vacuum device well enough to have a toaster oven in his shop, melt the HDPE, then remove it form the oven and put it in the vacuum chamber and vacuum away. It would not vaporize so there's no worry of fumes, just froth. MAKE SURE your mold or container in which you melt the HDPE is at least twice the volume of the HDPE melt so your melt doesn't run over and mess up his/her vacuum chamber's intake or whatever. HDPE froth all over the place wouldn't be a nice thank you for a willing jeweler and YET another sixpack of his/her choice or bottle of vino de jour might cost you more.

Regarding turning and large HDPE items above, definitely welding pieces together by melting both sides to be fused is whatcha gotta do to ensure a good bond. Melted plastic should ooze from the joint when pressed together and the two pieces should be stabilized or clamped to ensure a real voidless bond until the plastic cools hard. I did this several times on the super ergo models in my gallery to make the index finger hole/module and pinkey rests...worked fine...got the idea from Matt (*you'llshootyoureyeout"). He uses a heat gun, I don't have one, so used carefully a propane torch played over the surface with care not to burn or ignite the plastic, just melt it good. I advise a heat gun and care to not over heat the plastic, it may produce a brittleness you don't want.

In working with two HDPE melts and four sling shot projects made from them, and being also pretty adept at wood shop, I would not hesitate to turn HDPE...at least give it a shot. Since it's not exactly the rigidity of wood, the tail stock may cut and the plastic piece break lose and the piece fly all around the shop or in yo' face...just don't hog much material with the lathe chisel so as to lessen tail stock stress and lessen the likelihood of the work breaking lose and hopping all around the shop. Wood sort of breaks off when the chisel is applied whereas HDPE might "grab" since it won't break off in chips. It would produce long spirals likely and if too much was hogged off it may want to "grab" the chisel and all sorts of funny stuff may result from a kick back of the lathe chisel in your chest or groin (a job as a tenor in the Mormon Tabernacle Choir?), or the piece breaking lose from the tail stock and scampering around the shop for a while.

Also, I pound the tail stock into the wood with a wooden mallet, but with HDPE, I doubt you'll be able to pound a tail stock into it, it's VERY LIKELY to be too resistant and resilient for the tail stock to penetrate well, so the problem exists of how to get the tail stock's four blades and center spike into the HDPE to give it enough purchase to turn it. Caveat on turning HDPE in a wood lathe. Possibly without destroying the temper of the tail stock, you could heat the tail stock to about 360deg F or 169ish C using an infrared temperature instrument to "see" on the digital screen the temp, then place it in the center of the HDPE billet to turn, then using pressure on the tail stock, with gloves of course, melting its way into the plastic for a firm grip. These suggestions are only ideas I have not tried...no guarantees.

If the piece starts to slow down or wobble in rotation, stop...it means the tail stock is cutting through it's grip and it's about to make a flight tour of the shop. It's the same principle as turning a very soft wood. HDPE may not be of risk but I thought I'd mention it in case it is. I never turned HDPE, only machine grade PVC and machine grade nylon in my metal lathe...with no prob but a metal lathe grips the piece, i.e. round stock, and rod or round stock is not a big chunk like you're talking about, with three powerful jaws, not a tail stock. The larger diameter the rotating work the more stress by leverage is applied to the tail stock grip. Physics.

If you are careful when you melt your HDPE chips, and don't melt pieces which are not flat, that is, prone to capture air, your bubbles won't be as prolific. If you make sure the plastic chips you added are thoroughly melted before adding more, likewise you lessen the likelihood of voids or captured air. If you melt a whole gob of chips on top of chips likely you'll get more bubbles/voids. Let a layer of chips melt thoroughly, say half an hour or so before adding another layer to reduce voids/bubbles. For a 1.4 inches thick billet I melted nine layers of chips a half hour each, lots of patience and time here. Might advise buying slabs and welding them together but if you want the tie dye effect of multicolored chips, melt away. Bottle caps and other cup shapes will capture air if inverted on top of the melt when adding plastic to the melt.
Also in the bubble subject of this thread, not all stuff that's marked HDPE is the same HDPE. One of my melts was rock solid, no voids/bubbles, the other was littered with bubbles. The problem arose from some of the plastic being (I think) already recycled and likely contained low density poly (LDPE) which likely has a lower melting point and therefore likely a lower vaporizing point...or had other plastics other than polyethylene in the mix...resulting in gas bubbles from SOMETHING vaporizing. . The melt temp was the same for both batches. I've heard of other HDPE makers with the same problem, which is why some use new poly but cheap items bought at stores. It doesn't take much HDPE to make a nice SS...so a few bucks spent on, say, buckets or the like isn't much of a consideration. Make sure your plastic chips are absolutely squeaky clean, preferably new plastic free from dirt and oils, shampoo goop and food stuff.

Vacuum/resin stabilized wood:
By the way if you become a slingshot making addict as many of us are, a vacuum machine is good for impregnating wood frames/forks with plastic or epoxy resins to plasticize them making for waterproof durable frames...by immersing a wood item in a tub of resin, vacuuming the wood item to extract as much air from the wood cells as possible, keeping the vacuum going for a while until no more bubbles appear in the bath of resin, then releasing the vacuum to let ambient 14.7lbs/sq.inch (or there abouts in X altitude) air pressure to force the resin into voids previously occupied by air, plasticizing the item inside and out. You will have to weigh the item down to prevent it from floating in the resin, likely with a lead bar or lead weight. It will be somewhat of a messy operation and you won't use all the resin so some is wasted. It's best to save up items to plasticize (called "stabilize" sometimes) and do a large batch for resin efficiency since you can't save catalyzed resin OR have something to cast out of the left overs, fast, before it gels. Catalyzed resins start to gel in about 20-30 minutes depending on temperature and how much catalyst you add to the mix.
The most common use of this is making kitchen knife handles and knife scales. Further more you "might can" (old south eeze) offer a service to forum members to impregnate wood billets for sling shots with polyester resin or epoxy. The more liquid the resin the more it will penetrate and plasticize a wood item...epoxy is pretty goopy whereas polyester resin and urethane varnish is pretty liquid. I wonder how vacuum'd linseed oil treatment would work on wood? Linseed oil polymerizes in wood to become solid somewhat like a resin.

Chuck


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