How to cut soap consistently well?

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Garden Gives Me Joy

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How do you manage to consistently cut straight, parallel lines using a guillotine to make bars correctly reflect your label's stated weight?

After figuring that weight loss of bars for one of my recipes is 4%, I aim to cut bars at 104% to 105% of the label weight. Do you do this? Using the guillotine below (with the red arrow in it), the results have been disastrous. For instance, when cutting, some bars are either way too high like 150% or just below at around 97% - 98%. What do you do with your imperfect 150% and 97% soaps? It seems messy to price each bar on its unique weight. Also, the non parallel nature of the lines in some instances is so obvious that won't it simply look too unprofessional? Are moderately non parallel soaps acceptable to customers ... or just seem too unprofessional (even for a newbie seller)?

Will a new guillotine with an adjustable piece (as pictured in the image with a circle in it), resolve my problems with non parallel lines? ... and or do I need to improve my technique of properly anchoring the soap as I cut it?

I could ask a wood worker in the area to build a new guillotine. My log molds produce bars with dimensions of 3.25 by 2.25. Would the dimensions of the last image be good for resolving my problems? (Of course the wood worker will include the adjustable piece despite the fact that this 3rd image if my current guillotine does not show it). Happy to see your designs or design ideas.

one other nuisance is that the knife sometimes gets stuck as opposed to sliding all the way to the bottom. In such cases, it is cutting into the wood of the inside of the slot. Should the slot be thinner?

Also was wondering if it would be a good idea to also make one of the long sides adjustable ... or whether that would be an overkill without any benefit. If anyone wondered why I thought of having 3.5" tall walls; it is because I wanted the option of cutting with the soap oriented the portrait way. Currently, the walls are too short to accommodate that.

BTW, regarding wire cutters. Is it ever possible to adjust strings on the wire cutters to different widths, ie if one needs to cut specific weights?
 

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I do it round the other way - I cut, cure and then weigh my soaps. Out of a loaf - which is usually 11 bars - I can get about 8 or so that are between 115 - 120g, maybe one or two of those might be 122g, then the other few end up about 107 or 108 g. So I pick the ones that are all over 115g and list them on my website as being 'minimum 115g'. Then I take all the underweight ones to my market stall once a month and sell them there at a cheaper rate.
The odd freak - a highly overweight bar - I might keep for myself, or when a favourite customer places an order they get that one instead of the advertised weight.
I don't pre-print labels with weights on though - so I realise that's a difference between our processes.
 
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I am no help with how to cut straighter bars; my cutting skills are so bad that I shelled out the $$$ for a multi-bar string cutter from Nurture. The advantage is near perfect cuts; the disadvantage is the lack of adjustable widths. Since you need adjustable widths, a single-wire cutter with an adjustable stop sounds like your best bet to me.
 

DeeAnna

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If your miter-box cutter isn't making parallel cuts and the bar weights are varying a lot, one reason is the slots your cutter slides through are too wide. The slot width needs to be reduced to a snug fit. Also the slots might not be exactly opposite each other which will cause the cut to be angled.

Another reason for weight variations is the top of the loaf isn't level. High swoopy or ruffled tops will obviously reduce the consistency of the bar weights. But even a flat-topped loaf can have problems if the middle is crowned -- slightly higher than the ends. Even the most accurate cutter in the world can't overcome these issues.

I've used a miter-box cutter, but I get the best results with a wire cutter. Assuming I'm cutting a loaf of soap that is a fairly consistent height, the bar weights will be like Kiwi's -- within about 5 grams of my target.
 

earlene

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I have a couple of questions, some references for figuring out expected weight loss of soap based on recipe and some information or suggestions regarding the non-uniformity of your cut soap sizes, as well as information about adjustable multi-bar cutters.

I have used a mitre-box type cutter and like Ali-Oop, switched to a wire cutter for more uniform sizes of my cut soaps from loaves & slabs.

But, there may be a way to make the slots in your guillotine thinner so as to acheive less sloppy movement of the cutter (knife or bench scraper or whatever you use) while cutting your soap. Having never tried this, I don't really know how well it may work, or if it's even worth the trouble, but here goes....

First look at how much play there is when your cutter is in the slots. In other words, how much movement back & forth (including angled movement) do you have with the cutter? Is it 1/8 of an inch? More? Less? Once you figure that out, perhaps you can insert something flat that reduces the sloppy movement. The difficulty would probably be finding the right sized item, and securing it in place so that it doesn't move around as you use it or clean it between uses. Yeah, it might no be worth the effort. Probably why I chose the easier softer way and bought a wire cutter.

Questions: Why do you pre-print weights when your experience tells you, you don't cut uniform sizes? Or since you know your lowest weight is 'x', why not just label all soaps at that lowest weight? Another option would be to leave the weight blank and hand-write the weight after you package the soap. How do you estimate your soap weight after cure?

Links to figuring out soap weight after cure (maybe this is already how you do it):

Regarding adjustable width multi-bar soap cutters:

Here is one which can be purchased from Tennessee in the US: » Adjustable Multi-Cutter, Adjustable Soap Cutter
Soap width can vary by 1/4 inch increments. With the extra wires, one could use this cutter to cut hotel guest sized soaps as well as larger bars of soap by placing the wires further apart.
Here is a video on changing the wires to for various widths of soap bars:


Here was a discussion at SMF about how to design one: Adjustable multi wire soap log cutter - any interest? Need design suggestions
 

xyxoxy

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I don't make soaps to sell (though that may change one day soon) so I don't care as much about exact uniform weights. But I do like consistent appearance so I will also jump on the bandwagon that wire cutters are more precise and predictable. I use one made by my dad that is similar in design to the one shown in the Youtube video posted by Earlene.
 

TheGecko

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I never liked those miter boxes...too much play in the cut line(s) because they are made to used with crinkle cutters. I bought a cheese slicer and then modified it by gluing on a dowel so I could hold the loaf without slippage. Eventually I purchased a single-bar cutter from someone's destash.

Now something you might try is to remove the guide at the end and then measure from the end of the box to the width and put a piece of tape or mark and then use the end of the box to cut your soap:

Soap Box.png



A constant weight can be an issue even with a perfectly flat soap and a single-bar or multi cutter. I cure my soap in my garage for a minimum of six weeks and depending on the time of year, weather conditions, how much soap is on the tray, how much laundry I have done...the weight of my soap can vary, and of course, soap continues to 'cure'. I just weighed a bunch of soap out of my garage and they all weighed slightly different. I did have two bars that weighed under my selling weight, but they are soap that's been sitting on the top shelf for almost two years...the fragrance was discontinued so it's "me" soap that I grab ever so often. Even the last of my husband's soap that is a year old is still over my selling weight and that's all I can about.
 

Garden Gives Me Joy

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Image of miter box cutter below is what the hardware store guy sent me via WhatsApp re miter box cutters. However, he does not know much about the cutter. Would be happy for your thoughts to save me a possibly wasted trip to the store.

Can someone else please tell me whether the hole, projection at the bottom of the frame or something else usually has some type of adjustable stop mechanism that will allow me to make bars of roughly 1-inch thick? I see one set of slots just above the product label. Should I imagine that there is a second one hidden below the label? If not, is there some way this will allow me to make 1-inch thick bars? .... or should I just ask the woodworker to custom make a box cutter instead?
WhatsApp Image 2022-07-25 at 4.50.43 PM.jpeg
 

River

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Image of miter box cutter below is what the hardware store guy sent me via WhatsApp re miter box cutters. However, he does not know much about the cutter. Would be happy for your thoughts to save me a possibly wasted trip to the store.

Can someone else please tell me whether the hole, projection at the bottom of the frame or something else usually has some type of adjustable stop mechanism that will allow me to make bars of roughly 1-inch thick? I see one set of slots just above the product label. Should I imagine that there is a second one hidden below the label? If not, is there some way this will allow me to make 1-inch thick bars? .... or should I just ask the woodworker to custom make a box cutter instead?
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So, the other day I just happened to have bought the same Stanley miter box from Harbor Freight for a construction project. I think it would work as a soap bar cutter. The angle is true and the bottom is flat, except for the cut line, which is depressed, ensuring a complete through cut. I put my hand blade in the 90-degree slot. It fit and there was very little play. There are inch and centimeter markings on the sides which you could use to measure your cuts. One possible drawback is that the base has several holes in it, but that would only effect narrow loaves. For the usual 3" to 3.5" loaf, that wouldn't be an issue and might not be for even narrower loaves. Hope this is helpful.
 

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Garden Gives Me Joy

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Is there a significant advantage to using a hand blade with the design that @River uses (ie with the handle above)?

I can not currently find a stainless steel hand blade other than one for the equivalent of USD 10 at my supplier through whom I am preparing to make an order. Should I buy it ... or would a heavy stainless steel bread knife suffice?

So thankful for the support of this group!
 
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I find the pastry knife (bench scraper, dough knife - the thing in the pic above) does a much better job than a bread knife, mostly because any regular knife will be thin at the blade's edge, and widen towards the top. It usually widens from tip to handle, as well. That creates angled cuts and increases the likelihood of splitting/cracking the bar as you cut it. The pastry knife is usually an even thickness from top to bottom and side to side, and just slightly thinner on the scraping edge.

I found a cheap pastry knife at a local thrift store; I think it was $2? Might be worth a look. :)
 
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earlene

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I used a mitre box & a drywall knife for cutting soap for awhile. I posted about it here:


None of the 3 pastry knives I own would reach the bottom of the mitre box, because the rounded part prevents them from going deep enough to the bottom of the cutting area, which is why I bought the drywall knife.

To make the soap move more smoothly along the bottom surface of the box, I cut a plastic placemat to fit the width of the bottom surface.

The only problem had with that set-up was that there was still too much play between the slots and the knife, which lead to not enough uniformity in the width of my soaps. They were not always equal, nor were they always perfectly straight. Perhaps with better hand control, and a better eye for a straight cut, others can manage that better, but I just cannot cut straight!

For uniformity of width, you can simply put a mark on the box with either permanent marker or masking tape (I prefer the latter) to measure your soap width for the cut. Or you can add a 'stop' via inserting a block of wood where you want the soap to stop when you push through to where you will cut. If you look at a single bar soap cutter such as this one, the 'stop' is pictured. Example of one made of wood, with the 'stop' circled in yellow. You don't need a design as intricate, though. Anything wedged or secured to stop the loaf from advancing would work. Or you could just push it to a masking tape line and hold it with your hand.
1659553047044.png
 
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AAShillito

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I guess as others have suggested the best and most consistent way is a multi bar wire cutter. I saved up over a few months for a custom 1.25" cutter from Nurture Soaps. Barbie is worth every penny and saved so many tears and cussing with my miter box. I also do similar to @KiwiMoose And dont weigh until its cured. I just print off the labels and handwrite weights
 

Relle

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We use to have a knife shop and before Dh made me a cutter I would use a ham knife to cut my soap. They are the same thickness along to the handle and are flexible. I marked each edge of the soap the thickness I wanted and cut through from the top carefully making sure it was lined up. It takes longer than a cutter but definitely works if you take your time. My soap was consistantly the same thickness. I still use a knife with a slab mould.
 

Relle

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I had no idea there was a dedicated ham knife, @Relle. Now I have to go Google 'ham knife'. LOL Amazing the things I learn here at SMF!
Earlene, this is the one we have, it's Victorinox, they are not cheap but dh has been using this brand of knives for work since he was an apprentice. As you can see the blade goes right through the handle and is pinned. As a cutler ( has made his own knives) he still uses these commercial ones at home (probably because we have so many) :D.
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